Genetics Chapter 11

Gregor Mendel  “Father” of genetics  Austrian monk, mid-1800s  Researched pea plant inheritance –Easy to grow, fast reproduction –Studied plant height, pea shape/color, pod color, etc.

Pea Plant Reproduction  Self-pollination –Male gametes (pollen) fertilize egg of same flower –Produces pure-bred offspring –True-breeding: produce offspring identical to parent when self-pollinated

Pea Plant Reproduction  Cross-pollination –Pollen from one plant fertilizes egg of another plant –Offspring have two parents

Mendel’s Experiments  P = Parent generation  F 1 = First filial generation  F 2 = Second filial generation (F 1 X F 1 ) P Pure Green X Pure Yellow F 1 All Green F 2 3 Green:1 Yellow

Mendel’s Conclusions  Law of Dominance – one allele (form of a gene) is dominant, one is recessive –Recessive trait was hidden in F 1 generation –Green = dominant –Yellow = recessive

Mendel’s Conclusions  Law of Segregation: alleles for a gene separate when gametes form (meiosis I) –Each gamete gets one copy of each gene

Some Vocab.  Genotype – allele combination –Capital letter = dominant allele –Lowercase letter = recessive allele –Ex – AA, Aa, aa  Phenotype – physical appearance –Ex – green, yellow

Some Vocab.  Homozygous – two alleles same –Homozygous dominant: AA –Homozygous recessive: aa  Heterozygous – two alleles different –Aa

Punnett Squares  First must determine possible gametes  Heterozygous tall plant = Tt –Half of gametes will get ‘T’, other half will get ‘t’  Homozygous tall plant = TT –All gametes will get ‘T’

Punnett Squares  Monohybrid cross –Cross involving one trait  Gametes go on the top and side  Combine gametes to find possible offspring Tt X Tt

Punnett Squares  Genotype ratio 1TT: 2Tt: 1tt  Phenotype ratio 3 tall: 1 short Tt X Tt

Probability  Punnett squares are used to predict the probability of certain traits in offspring of genetic crosses  Tt X Tt –½ chance of getting ‘t’ from mom, ½ chance of getting ‘t’ from dad –½ X ½ = ¼ tt in offspring

Dihybrid Cross  Mendel looked at the inheritance patterns of two traits –Seed shape and seed color  Found that the traits were inherited independently of each other  Law of Independent Assortment –Genes on separate chromosomes are inherited at random –Due to random chromosome shuffling in Metaphase I

Independent Assortment Metaphase I

Non-Mendelian Genetics  Not all traits follow Mendel’s Law of Dominance  Four Variations –Incomplete Dominance (blending) –Codominance (two phenotypes) –Multiple Alleles –Polygenic Traits

Incomplete Dominance  Neither allele is dominant, both produce a protein  Heterozygous phenotype is a blend of both homozygous phenotypes  Ex – wavy hair, pink flowers

Incomplete Dominance

Codominance  Neither allele dominates the other, both produce a protein  Heterozygous phenotype is a combination of both homozygous phenotypes  Ex – checkered chicken, human blood types,

Multiple Alleles  Some genes have more than two alleles  Each individual only gets two, but there are more than two in the population  Ex – Rabbit fur color

Multiple Alleles  Rabbit fur alleles (in order of dominance) –C: dark gray –c ch : chinchilla –c h : himalayan –c: albino

Multiple Alleles

Polygenic Traits  Many traits are controlled by more than one gene  Traits show wide variation  Ex – human height, IQ, bell pepper colors