development and inheritance

Development and Inheritance

Muse W12 2440 lecture # 134/18/12

Gestation

First Trimester Period of embryological and early fetal development Rudiments of all major organ systems appear

Second Trimester Development of organs and organ systems Body shape and proportions change

By end, fetus looks distinctively human

Third Trimester Rapid fetal growth and deposition of adipose tissue Most major organ systems are fully functional

The First Trimester

Figure 29–7a The First Trimester.

The First Trimester

Figure 29–7b The First Trimester.

What will I be when I grow up?

The First Trimester

Figure 29–7c The First Trimester.

The First Trimester

Figure 29–7d The First Trimester.

The Second and Third Trimesters

Second Trimester Fetus grows faster than surrounding placenta

Third Trimester Most of the organ systems become ready

Growth rate starts to slow

Largest weight gain

Fetus and enlarged uterus displace many of mother’s

abdominal organs


Figure 29–8a The Second and Third Trimesters: A Four-Month-Old

Fetus As Seen through a Fiber-Optic Endoscope.


Figure 29–8b The Second and Third Trimesters: Head of a Six-Month-

Old Fetus As Seen through Ultrasound.


Figure 29–9c, d Growth of the Uterus and Fetus.

Inheritance

Nucleated Somatic Cells Carry copies of original 46 chromosomes present in

zygote Genotype

Chromosomes and their component genes Contain unique instructions that determine anatomical

and physiological characteristics Derived from genotypes of parents

Phenotype Physical expression of genotype Anatomical and physiological characteristics

Inheritance

Homologous Chromosomes Members of each pair of chromosomes

23 pairs carried in every somatic cell

At amphimixis, one member of each pair is

contributed by spermatozoon, other by ovum

Inheritance

Autosomal Chromosomes

22 pairs of homologous chromosomes

Most affect somatic characteristics

Each chromosome in pair has same structure

and carries genes that affect same traits

Inheritance

Sex Chromosomes Last pair of chromosomes

Determine whether individual is genetically male or

female

Karyotype Entire set of chromosomes

Locus Gene’s position on chromosome

Inheritance

Figure 29–14 A Human Karyotype.

Inheritance

Alleles are various forms of given gene Alternate forms determine precise effect of gene on

phenotype

Homozygous Both homologous chromosomes carry same allele of

particular gene

Simple Inheritance Phenotype determined by interactions between single

pair of alleles

Inheritance

Heterozygous Homologous chromosomes carry different allele of

particular gene

Resulting phenotype depends on nature of interaction

between alleles

Strict Dominance Dominant allele expressed in phenotype, regardless

of conflicting instructions carried by other allele

Inheritance

Recessive Allele Expressed in phenotype only if same allele is present

on both chromosomes of homologous pair

Incomplete Dominance Heterozygous alleles produce unique phenotype

Codominance Exhibits both dominant and recessive phenotypes for

traits

Inheritance Penetrance

Percentage of individuals with particular genotype that show “expected” phenotype

Expressivity Extent to which particular allele is expressed

Teratogens Factors that result in abnormal development

Punnett Square Simple box diagram used to predict characteristics of

offspring

Mutation - change in normal form of gene

Inheritance

Figure 29–15 Predicting Phenotypic Characters by Using Punnett Squares.

Inheritance

Polygenic Inheritance Involves interactions among alleles on several genes Cannot predict phenotypic characteristics using

Punnett square Linked to risks of developing several important adult

disorders

Suppression One gene suppresses other Second gene has no effect on phenotype

Inheritance

Inheritance

Complementary Gene Action Dominant alleles on two genes interact to produce

phenotype different from that seen when one gene contains recessive alleles

Sources of Individual Variation During meiosis, maternal and paternal chromosomes

are randomly distributed Each gamete has unique combination of maternal and

paternal chromosomes

Inheritance

Genetic Recombination During meiosis, various changes can occur in

chromosome structure, producing gametes with

chromosomes that differ from those of each parent

Greatly increases range of possible variation among

gametes

Can complicate tracing of inheritance of genetic

disorders

Inheritance

Crossing Over Parts of chromosomes become rearranged during

synapsis

When tetrads form, adjacent chromatids may overlap

Translocation Reshuffling process

Chromatids may break, overlapping segments trade

places

Inheritance

Figure 29–17 Crossing Over and Translocation.

Inheritance

Genomic Imprinting

During recombination, portions of

chromosomes may break away and be

deleted

Effects depend on whether abnormal gamete

is produced through oogenesis or

spermatogenesis

Inheritance

Chromosomal Abnormalities Damaged, broken, missing, or extra copies of chromosomes

Few survive to full term

Produce variety of serious clinical conditions

Humans are poorly tolerant of changes in gene copy number

(to few or too many = lethal or bad news)

Mutation Changes in nucleotide sequence of allele

Inheritance

Spontaneous Mutations Result of random errors in DNA replication

Errors relatively common, but in most cases error is

detected and repaired by enzymes in nucleus

Errors that go undetected and unrepaired have

potential to change phenotype

Can produce gametes that contain abnormal alleles

Inheritance

Carriers Individuals who are heterozygous for

abnormal allele but do not show effects of

mutation

Inheritance

Sex Chromosomes X Chromosome

Considerably larger

Have more genes than do Y chromosomes

Carried by all oocytes

Y Chromosome Includes dominant alleles specifying that the individual will be

male

Not present in females

Autosomes, sex chromosomes and sex determination

Karyotype shows 46 chromosomes arranged in pairs by size and centromere position

22 pairs are autosomes – same appearance in males and females

23rd pair are sex chromosomes

XX = female XY = male

Inheritance

Sperm

Carry either X or Y chromosome

Because males have one of each, can pass

along either 50% chance of each

Inheritance

X-Linked Genes that affect somatic structures

Carried by X chromosome

Inheritance does not follow pattern of alleles on

autosomal chromosomes

Sex determination

Males produce sperm carrying an X or Y Females only produce

eggs carrying an X Individual’s sex determined

by father’s sperm carrying X or Y

Male and female embryos develop identically until about 7 weeks Y initiates male pattern of

development SRY on Y chromosome

Absence of Y determines female pattern of development

Inheritance

Figure 29–18 Inheritance of an X-Linked Trait

Inheritance of red-green color blindness

Sex-linked inheritance

Genes for these traits on

the X but not the Y

Red-green colorblindness Most common type of color

blindness

Red and green are seen as

same color

Males have only one X

– They express whatever they

inherit from their mother

Color blind

maleXcY

Normal maleXCY

Color blind

femaleXcXc

Normal

female

(carrier)

XCXc

Normal

femaleXCXC

PhenotypeGenotype

Inheritance

Human Genome Project Goal was to transcribe entire human genome

Has mapped thousands of human genes

Genome

Full complement of genetic material

Inheritance

Figure 29–19 A Map of Human Chromosomes.

Inheritance

Passage of hereditary traits from one generation to the next

Genotype and phenotype Nuclei of all human cells except gametes contain 23

pairs of chromosomes – diploid or 2n One chromosome from each pair came from father,

other member from mother Each chromosome contains homologous genes for

same traits Allele – alternative forms of a gene that code for the

same trait Mutation – permanent heritable change in allele that

produces a different variant

Inheritance

Phenylketonuria or PKU example

Unable to manufacture enzyme phenylalanine hydroxylase Allele for function enzyme = P Allele that fails to produce functional enzyme = p Punnet square show possible combinations of alleles

between 2 parents Genotype – different combinations of genes Phenotype – expression of genetic makeup

PP – homozygous dominant – normal phenotype Pp – heterozygous – normal phenotype

– 1 dominant allele codes for enough enzyme– Can pass recessive allele on to offspring – carrier

pp - homozygous recessive – PKU– 2 recessive alleles make no functional enzyme

Inheritance

Alleles that code for normal traits are not always dominant Huntington disease caused by dominant allele

Both homozygous dominant and heterozygous individuals get HD

Nondisjunction Error in cell division resulting in abnormal number of

chromosomes Aneuploid – chromosomes added or missing

Monosomic cell missing 1 chromosome (2n-1) Trisomic cell has additional chromosome (2n +1)

– Down Syndrome – trisomy 21 – 3 21st chromosomes

Variations of Dominant-recessive inheritance

Simple dominance-recessive

Just described where dominant allele covers effect of

recessive allele

Incomplete dominance

Neither allele dominant over other

Heterozygote has intermediate phenotype

Sickle-cell disease

Sickle-cell disease

Sickle-cell disease

HbAHbA – normal

hemoglobin

HbSHbS – sickle-cell disease

HbAHbS – ½ normal and ½

abnormal hemoglobin Minor problems, are carriers

for disease

Incomplete Dominance

Heterozygous individuals have an intermediate phenotype

Example: Sickling gene SS = normal Hb is made Ss = sickle-cell trait (both aberrant and normal

Hb are made); can suffer a sickle-cell crisis under prolonged reduction in blood O2)

ss = sickle-cell anemia (only aberrant Hb is made; more susceptible to sickle-cell crisis)

Figure 17.8b

1 2 3 4 5 6 7 146

(b) Sickled erythrocyte results from a single amino acid change in the beta chain of hemoglobin.

Multiple-allele inheritance

Some genes have more

than 2 alleles

ABO blood group

IA produces A antigen

IB produces B antigen

i produces neither

A and B are codominant

– Both genes expressed

equally in heterozygote

OIi

ABIA IB

BIB IB or IB i

AIA IA or IA i

Phenotype

(blood

type)

Genotype

Blood type inheritance

Complex inheritance

Polygenic inheritance – most inherited traits not controlled

by one gene

Complex inheritance – combined effects of many genes

and environmental factors

Skin color, hair color, height, metabolism rate, body build

Even if a person inherits several genes for tallness, full height

can only be reached with adequate nutrition

Neural tube deficits are more common if the mother lacks

adequate folic acid in the diet – environmental effect

Skin color is a complex trait

Depends on

environmental conditions

like sun exposure and

nutrition and several

genes

Additive effects of 3 genes

plus environmental affect

produces actual skin color

Polygene Inheritance of Skin Color

Alleles for dark skin (ABC) are incompletely

dominant over those for light skin (abc)

The first-generation offspring each have three

“units” of darkness (intermediate pigmentation)

The second-generation offspring have a wide

variation in possible pigmentations

Figure 29.3 (1 of 4)

H Allele for brown hairh Allele for blond hair

E Allele for brown eyese Allele for blue eyes

Paternal chromosome

Maternal chromosomeHomologous pair

Hair color genes Eye color genes

Homologous chromosomes synapse duringprophase of meiosis I. Each chromosome consistsof two sister chromatids.


H Allele for brown hair

h Allele for blond hair

E Allele for brown eyes

e Allele for blue eyes

Paternal chromosome


One chromatid segment exchanges positions with a homologous chromatid segment—in other words, crossing over occurs, forming a chiasma.

Chiasma






Paternal chromosome


The chromatids forming the chiasma break, and the broken-off ends join their corresponding homologues.

Random Fertilization

A single egg is fertilized by a single sperm

in a random manner

Because of independent assortment and

random fertilization, an offspring represents

one out of 72 trillion (8.5 million 8.5

million) zygote possibilities






Paternal chromosome


At the conclusion of meiosis, each haploid gamete has one of the four chromosomes shown. Two of the chromosomes are recombinant (they carry new combinations of genes).

Gamete 1

Gamete 2

Gamete 3

Gamete 4

Environmental Factors in Gene Expression

Phenocopies: environmentally produced phenotypes that mimic conditions caused by genetic mutations

Environmental factors can influence genetic expression after birth Poor nutrition can affect brain growth, body

development, and height Childhood hormonal deficits can lead to

abnormal skeletal growth and proportions

Nontraditional Inheritance

Influences due to

Genes of small RNAs

Epigenetic marks (chemical groups attached

to DNA)

Extranuclear (mitochondrial) inheritance

Small RNAs

MicroRNAs (miRNAs) and short interfering RNAs

(siRNAs)

Act directly on DNA, other RNAs, or proteins

Inactivate transposons, genes that tend to replicate

themselves and disable or hyperactivate other genes

Control timing of apoptosis during development

In future, RNA-interfering drugs may treat diseases

such as age-related macular degeneration and

Parkinson’s disease

Epigenetic Marks

Genomic imprinting tags genes as

maternal or paternal and is essential for

normal development

Allows the embryo to express only the

mother’s gene or the father’s gene

Epigenetic Marks

Information stored in the proteins and

chemical groups bound to DNA

Determine whether DNA is available for

transcription or silenced

May predispose a cell to cancer or other

devastating illness

Epigenetic Marks

The same allele can have different effects

depending on which parent it comes from

For example, deletions in chromosome 15

result in

Prader-Willi syndrome if inherited from the father

Angelman syndrome if inherited from the mother

Extranuclear (Mitochondrial) Inheritance

Some genes (37) are in the mitochondrial DNA

(mtDNA)

Transmitted by the mother in the cytoplasm of the

egg

Errors in mtDNA are linked to rare disorders:

muscle disorders and neurological problems,

possibly Alzheimer’s and Parkinson’s diseases

Sins of the father? Epigenetics at workScientists at Australia’s University of New South Wales fed healthy, svelte, male rats a high-fat diet (43 percent of calories from fat—a typical American diet). Not surprisingly, the rats put on weight and fat, and developed insulin resistance and glucose intolerance—basically, type 2 diabetes, the scientists reported last month in Nature. None of that was surprising. What made the scientists take notice was the daughters these rats sired: although their mothers were of normal weight and ate a healthy diet while pregnant, daughters of the high-fat-diet dads developed insulin resistance and glucose resistance as adults—even though they never ate a high-fat diet themselves.Mothers’ diet while pregnant affects their children’s health as adults because of how nutrients and toxic compounds pass through the placenta. But fathers have no contact with their daughters except through the sperm that created them. These rat fathers were not genetically diabetic. The conclusion is therefore inescapable: the fathers’ high-fat diet altered their sperm in a way that induced adult-onset disease in their daughters.

development and inheritance

Documents