CHAPTER 10 SEXUAL

REPRODUCTION AND GENETICS

• SECTION 10.1 – MEIOSIS• MAIN IDEA – MEIOSIS PRODUCES HAPLOID

GAMETES.–All of the differences you see in the room,

different hair color, eye color, ear shapes, is the result of 2 sex cells combining during sexual reproduction.

• QUESTION: How are the following cell parts involved in mitosis?–Chromosome, spindle fibers, nucleus, and

nucleolus

• CHROMOSOMES AND CHROMOSOME NUMBER• Everyone has characteristics passed on to them

from their parents.• Each characteristic is called a trait.– Ex: hair color, height or eye color

• The instructions for each trait are located on the chromosomes, which are found in the nucleus of cells.

• The DNA on the chromosomes is arranged in segments called genes that control the production of proteins.– Each chromosome has 100’s of genes.

• HOMOLOGOUS CHROMOSOMES• Human body cells (somatic cells)

have 46 chromosomes.– Each parent gave you 23 chromosomes creating 23

PAIRS of chromosomes or 46 chromosomes.• The chromosomes that make up a pair (the one from

mom & the one from dad) are called homologous chromosomes– Homologous chromosomes in body cells have the

same length, same centromere position, and carry genes that control the same inherited traits.• These genes each code for the same trait (ex:

earlobe) but maybe not the same type of trait (earlobe)

• HAPLOID AND DIPLOID CELLS• Gametes are sex cells that have half the number of

chromosomes.– In humans the number of chromosomes in a gamete is 23.• Each species has a different # of chromosomes

– The symbol n can be used to represent the number of chromosomes in a gamete.• Cells with n number of chromosomes is called a haploid

cell.–Haploos means single.

• Fertilization is the process by which one haploid gamete (egg) combines with another haploid gamete (sperm)– Fertilization creates cells that are 2n (one n chromosome

from mom & one n chromosome from dad)– 2n cells are called diploid cells

• MEIOSIS I• Gametes are formed during a process called meiosis.– Meiosis is a type of cell division that reduces the number

of chromosomes– Meiosis is a reduction division.• Mitosis maintains the chromosome #, meiosis

reduces the chromosome # by half through the separation of homologous chromosomes.• Cells begin as 2n, but create gametes with n number

of chromosomes– Meiosis occurs in the reproductive structures of

organisms that reproduce sexually.• Meiosis involves 2 consecutive cell divisions called meiosis I

& meiosis II

• INTERPHASE• Just like with mitosis, cells that

undergo meiosis also go through interphase as part of their cell cycle.–While in interphase cells carry out

various metabolic processes, including the replication of DNA and the synthesis of proteins

• PROPHASE I• Cells entering prophase I, the replicated (copied)

chromosomes become visible.–Creating sister chromatids

• Homologous chromosomes (mom’s sister chromatid + dad’s sister chromatid) form during synapsis and are held tightly together. Can be called a tetrad.–Crossing over occurs this time.

• Crossing over is a process when segments of chromosomes are exchanged between a pair of homologous chromosomes.

• Prophase I continues with the centrioles moving to the cell’s opposite poles, spindle fibers forming and binding to the sister chromatids at the centromere.

• PROPHASE I

• METAPHASE I• 2nd phase of meiosis• Homologous chromosomes line up at the

equator of the cell.• Spindle fibers are attached to the

centromere of each homologous chromosome

• ANAPHASE I• During anaphase I homologous chromosomes

separate.–Sister chromatids are pulled to opposite

poles of the cell–Chromosome number is reduced from 2n to n when the homologous chromosomes separate.

• TELOPHASE I• Homologous chromosomes (sister chromatids)

reach the cell’s opposite poles.– Sister chromatids are still joined at the

centromere– Sister chromatids might not be identical from

when it started because of crossing over.–During telophase I, cytokinesis usually occurs

pinching in the animal cell or forming cell plate in plant cells.–May or may not go into interphase. If cell goes

into interphase, DNA is NOT duplicated again.

• Telophase I

• MEIOSIS II• Meiosis is only half done after meiosis I.• Prophase II the sister chromatids condense and

spindle apparatus forms• Metaphase II the sister chromatids line up at the

equator by the spindle fibers.• Anaphase II the sister chromatids are pulled apart

at the centromere by the spindle fibers and the chromosomes move toward the opposite poles of the cell.

• Telophase II the chromosomes reach the poles and the nuclear membrane and nuclei reform.

• At the end of meiosis II, cytokinesis occurs creating 4 haploid cells each with n number of chromosomes

• MEIOSIS II

• MEIOSIS PROVIDES VARIATION• Genetic variation is produced during crossing over and

during fertilization when gametes randomly combine.• Depending on how chromosomes line up at the equator, 4

gametes with 4 different combinations of chromosomes can result.

• SEXUAL REPRODUCTION VS. ASEXUAL REPRODUCTION• Asexual reproduction the organism inherits all of its

chromosomes from a single parent and are genetically identical to the parent.– Ex: bacteria

• Sexual reproduction allows variation and beneficial mutations to accumulate faster in the population.

• SECTION 10.2 – MENDELIAN GENETICS• MAIN IDEA – Mendel explained how a

dominant allele can mask the presence of a recessive allele.

• QUESTION: Do all dogs look alike?• What types of features indicate a particular

breed?• Are these features inherited?• What does this tell you about the inheritance

of these features?

• HOW GENETICS BEGAN• In 1866 Gregor Mendel, an Austrian monk,

published a book on the method of inheritance in garden pea plants.

• Inheritance or heredity is the passing of traits from one generation to the next.

• Mendel chose pea plants to study because they are true-breeding, meaning that they consistently produce offspring with only one form of a trait.– EX: always purple flowers

• Pea plants self-pollinate, but Mendel began to cross-pollinate the pea plants.

• THE INHERITANCE OF TRAITS• Mendel noticed that some varieties of peas

produced a specific form of a trait generation after generation.–EX: always green seeds or yellow seeds

• Mendel cross-pollinated (male gamete of one plant & combined with female gamete of the other plant)–Mendel referred to the male gamete &

female gametes used in the cross-pollination as the P generation or the parent generation.

• F1 AND F2 GENERATION• Mendel grew the seeds from the cross from the parent

generation (P generation), one green seed and one yellow seed and the results were all the offspring had yellow seeds.– The offspring from the parent generation (P generation)

are called the F1 generation or first filial generation.• Mendel questioned if the green seed was gone or being

hidden or masked.• Mendel planted the F1 generation and allowed them to

self-pollinate and then examined the seeds from this cross.– The offspring from the F1 generation is called the F2

generation or second filial generation.– Mendel’s results were a 3:1 ratio of 6022 yellow seeds

to 2001 green seeds

• GENES IN PAIRS• Mendel concluded there must be 2 forms of the

seed trait in pea plants – yellow and green seeds.• Allele is an alternative form of a single gene passed

from generation to generation.• Gene for yellow seeds and the gene for green seeds

are each different forms (alleles) of a single gene.• In Mendel’s experiments the yellow seed color was

dominant over the recessive green seed color.–Reason why the F1 generation was yellow and

explaining why the F2 generation had the 3:1 ratio of yellow to green

• DOMINANCE• When the dominant allele is present it will be the one that is shown.– Ex: Yellow seeds are dominant over the green seeds, results

shown in the F1 generation cross that Mendel made

• When modeling inheritance, the dominant allele is represented by a capital letter.– The letter used is the beginning letter of the dominant trait.• Ex: Yellow seeds used the capital Y• Ex: Round seeds dominant use capital letter R

• When modeling inheritance, the recessive allele is represented by a lower case letter.

• Homozygous for a particular trait means that the organism has the same 2 alleles.– Ex: homozygous (dominant) yellow seeds = YY– EX: homozygous (recessive) green seeds = yy

• DOMINANCE – CONTINUED• Heterozygous for a particular trait means

that the organism has 2 different alleles.–EX: one yellow allele and one green

allele = Yy •The dominant allele will always be expressed when the organism is heterozygous

• GENOTYPE AND PHENOTYPE• Genotype is the organisms allele pairs.–Ex: YY is the genotype for homozygous

dominant yellow seeds –Ex: Yy is the genotype for heterozygous

yellow seeds –EX: yy is the genotype for homozygous

recessive green seeds • Phenotype is the observable characteristic or

outward expression of an allele pair.–Ex: yellow seeds or green seeds

• MENDEL’S LAW OF SEGREGATION• Mendel’s Law of Segregation states that the 2

alleles for each trait separate during meiosis. –During fertilization the 2 alleles for that trait

unite.• Hybrids are

heterozygous organisms.

• LAW OF INDEPENDENT ASSORTMENT• Law of independent assortment states that a

random distribution of alleles occurs during gamete formation. Genes on separate chromosomes sort independently during meiosis.– Ex: an organism heterozygous for seed color (Yy)

crossed with another heterozygous organism (Yy) means that the Y allele and the y alleles from both organisms can recombine in any combination.• Either YY, Yy or yy

• PUNNETT SQUARES• Punnett squares are used to predict the possible

offspring of a cross between 2 known genotypes.• PUNNETT SQUARE – MONOHYBRID CROSS• The number of squares is determined by the number of

types of alleles produced by each parent.• Male gametes are written across the horizontal side.• Female gametes are written on the vertical side of the

Punnett square.• Possible combinations of each male and female gamete

are written on the inside of each corresponding square.– Dominant allele is written first, whether it comes

from the male or female gamete.

• PUNNETT SQUARE • Cross between heterozygous male (Bb) and a

heterozygous female (B)

• PUNNETT SQUARE – DIHYBRID CROSS• Dihybrid crosses is when we look at the inheritance

of 2 traits at the same time.– Ex: pea plants with yellow seeds (1trait) and round

seeds (1 trait)– If Mendel started with homozygous yellow round seeds

plant and green wrinkled seeds the F1 generation would be represented by YyRr

– Crossing the F1 generation yields a 9:3:3:1 ratio

• PUNNETT SQUARE – DIHYBRID CROSS

• PROBABILITY• The inheritance of genes can be

compared to the probability of flipping a coin.–Probability of the coin landing on heads

is 50% or half the time.–Large number of results makes it more

likely that the results will match the predicted results of the Punnett square

• SECTION 10.3 – GENE LINKAGE & POLYPLOIDY

• READ & TAKE NOTES OVER PAGES 283, 284, & 285.

• BE PREPARED TO SHARE YOUR NOTES WITH THE CLASS

• BE PREPARED TO TAKE A SHORT QUIZ OVER THESE PAGES