Mendelian Genetics. Vocabulary. M o l e c u l a r a n d M e n d e l i a n G e n e t i c s

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1 Mendelian Genetics Vocabulary Genotype: o Capital letter = allele o Lowercase letter = allele o Ex AA, Aa, aa Phenotype: o Ex green, yellow Homozygous: o Homozygous dominant: o Homozygous recessive: Heterozygous: o Gregor Mendel Austrian monk, mid-1800s Researched pea plant inheritance o Easy to grow, fast reproduction o Studied plant height, pea shape/color, pod color, etc. Pea plant reproduction o Male gametes (pollen) fertilize egg of flower Produces pure-bred offspring : produce offspring identical to parent when self-pollinated o Pollen from one plant fertilizes egg of another plant Offspring have parents Mendel s Experiments o P = generation o F 1 = generation o F 2 = generation (F 1 X F 1) o cross: cross involving one trait P Pure Purple X Pure White F 1 All Purple F 2 3 Purple:1 White 9

2 o cross: cross involving two traits Mendel studied seed and seed Found that the traits were inherited of each other P Pure Yellow/Smooth X Pure Green/Wrinkled F 1 All Yellow/Smooth F 2 9 Yellow/Smooth:3 Yellow/Wrinkled:3 Green/Smooth:1 Green/Wrinkled Mendel s Conclusions 1. Law of : one allele (form of a gene) is dominant, one is recessive trait was hidden in F 1 generation Purple = dominant White = recessive 2. Law of : alleles for a gene separate when gametes form Due to separation of in Anaphase I Each gets one copy of each gene 3. Law of : Genes on separate chromosomes are inherited at random Due to random in Metaphase I Metaphase I 10

3 Punnett Squares Used to show of certain genetic outcomes in offspring First must determine possible Heterozygous tall plant = Half of gametes will get T, the other half will get t Homozygous tall plant = All gametes will get T Gametes go on the top and side Combine gametes to find possible offspring Genotype ratio: Phenotype ratio: Monohybrid cross Dihybrid cross 11

4 Non-Mendelian Genetics Not all traits follow Mendel s Law of Dominance Four Variations o Neither allele is, only 50% of protein is produced o Heterozygous phenotype is a of both homozygous phenotypes o Ex wavy hair, pink flowers o Neither allele dominates the other, both produce a protein o Heterozygous phenotype is a of both homozygous phenotypes o Ex checkered chicken, human blood types, roan cattle o Some genes have more than o Each individual only inherits alleles, but there are more than two in the o Ex Rabbit fur color C: dark gray c ch : chinchilla c h : himalayan c: albino 12

5 o Many traits are controlled by o Traits show wide o Ex human height, eye color, bell pepper colors Linked Genes Each contains 100s of Those genes are said to be, because they are If genes are on chromosome, will happen frequently between them Genes are based on rate of crossing over Example o Genes A & B are completely linked Will not show o Genes A & C are incompletely linked Crossing over frequent o Genes A & D are unlinked Will show Human Genetics Quick Review chromosomes pairs of autosomes pair of sex chromosomes (circle it!) o = = genes base pairs 13

6 Blood Types Multiple alleles: Four phenotypes: Whose baby is it?? o Two couples had babies in the same hospital at the same time and the babies got mixed up. Doctors determine whose baby is whose using blood type analysis. The Johnson couple has blood types of B and AB; the Smith couple has blood types of B and A. Baby 1 has a blood type of A and Baby 2 has a blood type of O. Which baby belongs to which couple? Genetic Diseases and Pedigrees Pedigree: diagram used to show how in a family o Like a genetic family tree Cystic Fibrosis o Most common in Northern Europeans and their descendants 1/2500 births o Recessive disorder o Lungs clog with mucus, digestive problems 14

7 Sickle Cell Anemia o Most common in and their descendants o Protects against Malaria protist can t infect sickle cells o Better to be than to not carry the sickle cell allele in areas with malaria Sex-Linked Traits o carries 100s of genes o Since only have one X, they show X-linked alleles more often than females o Ex hemophilia, colorblindness, muscular dystrophy o Practice! What are the odds of a son being colorblind if his mom s dad was colorblind, but his mom and dad had normal vision? Allele for normal vision = X B Allele for colorblind = X b Mom s genotype = Dad s genotype = What pattern do you see in this pedigree? Why are only females heterozygous? 15

8 Sex Determination chromosome produces a protein that shuts off the chromosome o Leads to development Females only need one X, so extra X is shut off at random in each cell Nondisjuction o Turned off X called a Barr body o Leads to calico cats During metaphase I of formation, sometimes the don t separate Usually lethal, except in chr. 21 and sex chromosomes (13 & 18 rarely trisomy) o Extra 21 Trisomy 21 or Down Syndrome Turner Syndrome XO o Sterile, underdeveloped female Klinefelter s Syndrome XXY, XXXY o Sterile, long arms and legs, shy Triple X XXX Practice!! o Fertile, taller than average 1. Suppose that in outer space there exist creatures whose traits are inherited by Mendel s laws. You find purple eyes, P, are dominant to yellow eyes, p. Two purple-eyes creatures mate and produce six offspring. Four of them have purple eyes and two have yellow eyes. What are the genotypes of the parents? The phenotypes of the parents? What are the genotypes of the offspring? 2. In fruit flies, long wings, L, are dominant to short wings, l. Two long wing flies produce 49 short wing and 148 long wing offspring. What were the probable genotypes of the parents? What proportion of the long wing offspring should be heterozygous? 3. In certain species of plants, one purebred variety has hairy leaves and another purebred variety has smooth leaves. A cross of the two varieties produces offspring that all have smooth leaves. Predict the ratio of phenotypes and genotypes in the F 2 generation. 16