chromosomal basis of heredity
DESCRIPTION
Chromosomal Basis of Heredity. Studying Inheritance Patterns for Genes on Specific Chromosomes. Sex Determination. Sex Chromosomes : homologous chromosomes that differ in size and genetic composition between males and females. Autosomes. Autosome: any chromosome that is not a sex chromosome - PowerPoint PPT PresentationTRANSCRIPT
Chromosomal Basis of HeredityChromosomal Basis of Heredity
Studying Inheritance Patterns for Studying Inheritance Patterns for Genes on Specific ChromosomesGenes on Specific Chromosomes
Sex DeterminationSex Determination
Sex ChromosomesSex Chromosomes: homologous : homologous chromosomes that differ in size and chromosomes that differ in size and genetic composition between males and genetic composition between males and femalesfemales
Human Human
ChromosomeChromosome
XX YY
SizeSize LargerLarger SmallerSmaller
Genetic Genetic
CompositionComposition
Multiple Multiple
genesgenes
unrelated unrelated
to genderto gender
Very few Very few genesgenes
TDF region TDF region determines determines maleness maleness
AutosomesAutosomes
Autosome:Autosome: any chromosome any chromosome that is not a sex chromosomethat is not a sex chromosome
Humans have 22 pairs of Humans have 22 pairs of autosomes and 1 pair of sex autosomes and 1 pair of sex chromosomes chromosomes
XX11 XX22
Sex DeterminationSex Determinationin Mammalsin Mammals
EGGSEGGS
Male ParentMale ParentYYXXmm
SSPPEERRMM
Female OffspringFemale Offspring
Male OffspringMale Offspring
YY
XXmmXXmmXX11 XX22XXmm
YY YYXX11 XX22
Expected RatioExpected Ratio½ female: ½ male½ female: ½ male
XX11 XX22Female ParentFemale Parent
25%25%Red femaleRed female Red femaleRed female Red maleRed male
25%25% 25%25% 25%White male
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Sex Linked Genes: Eye Color in Fruit FliesSex Linked Genes: Eye Color in Fruit Flies
Eggs of Eggs of XR Xr FemaleFemale
Sperm ofSperm ofXXRRY Male Y Male
1111
YXR
XRXrXRXR
YXr
XRXR XrYXRXr XRY
R r
R
Female Female
Male Male
11 11
R = redR = redr = whiter = white
Sex-linked Genes in HumansSex-linked Genes in Humans
Hemophilic Male Non-hemophilic Hemophilic Male Non-hemophilic Female Female (father is hemophilic)(father is hemophilic)
XXhh
YY
XXHH X Xhh
XXHHXXhh XXhhXXhh
XXHHYY XXhhYY
Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring¼ hemophilic males + ¼ non-hemophilic males¼ hemophilic males + ¼ non-hemophilic males
¼ hemophilic females + ¼ non-hemophilic females¼ hemophilic females + ¼ non-hemophilic females
XXhhY x XY x XHHXXhhMales carry onlyMales carry onlyone copy of genes one copy of genes on the X chromosomeon the X chromosome
Females can beFemales can behomozygous or homozygous or heterozygous for heterozygous for traits on thetraits on the X chromosomeX chromosome
H = no hemophilia h = hemophiliaH = no hemophilia h = hemophiliaGrampsGramps
XXhhYY
Human Chromosomal AbnormalitiesHuman Chromosomal Abnormalities
Arise by Non-disjunction =Arise by Non-disjunction =Failure of homologues or chromatidsFailure of homologues or chromatidsto separate during meiosisto separate during meiosis
Normal MeiosisNormal Meiosis Non-disjunction Non-disjunction in Meiosis I in Meiosis I
Non-disjunction Non-disjunction in Meiosis II in Meiosis II
Human Autosomal AbnormalityHuman Autosomal Abnormality
How can Down Syndrome occur? How can Down Syndrome occur?
Eg. Egg with 2 copies of #21 Eg. Egg with 2 copies of #21 (24 chromosomes)(24 chromosomes)
+ Sperm with 1 copy of #21 + Sperm with 1 copy of #21 (23 chromosomes)(23 chromosomes)
= Embryo with 3 copies of #21 = Embryo with 3 copies of #21 (47 chromosomes)(47 chromosomes)
Down SyndromeDown Syndrome Trisomy 21Trisomy 21
Three copies of Three copies of chromosome 21chromosome 21
Incidence of Down Syndrome
1010 2020 3030 4040 505000
100100
200200
300300
400400
Age of Mother (years)Age of Mother (years)
Num
ber p
er 1
000
Birt
hsN
umbe
r per
100
0 B
irths
Karyotype for Down SyndromeKaryotype for Down Syndrome
Eye foldEye fold Palm CreasePalm Crease
Physical FeaturesPhysical Features
Human Sex Chromosome AbnormalityHuman Sex Chromosome Abnormality Turner SyndromeTurner Syndrome XOXO
One copy of XOne copy of X
No second sex No second sex chromosomechromosome
How can Turner Syndrome occur?How can Turner Syndrome occur?
Eg. Egg with 0 copies of XEg. Egg with 0 copies of X (22 chromosomes) (22 chromosomes)
+Sperm with 1 copy of X+Sperm with 1 copy of X (23 chromosomes) (23 chromosomes)
= Embryo with 1 copy of X= Embryo with 1 copy of X (45 chromosomes) (45 chromosomes)
Non-functional Ovaries From Adult Non-functional Ovaries From Adult Female with Turner’s SyndromeFemale with Turner’s Syndrome
Normal uterus, tubesNormal uterus, tubes and ovariesand ovaries
Karyotype for Karyotype for Turner’s SyndromeTurner’s Syndrome