Mendel and Heredity

Chapter 8

Heredity – the passing of characteristics from parents to offspring

Who was Gregor Mendel? • An Austrian Monk

• Parents were peasants, so he learned about agriculture very early on• he experimented breeding of different varieties of garden peas

Genetics – branch of biology that focuses on heredity

Mendel’s Peas

Studied 7 Different Traits (characteristics)

• trait = single form of a characterex. Purple flower

• character = inherited characteristicex. Flower color

Mendel = Father of GeneticsExperimented by crossing plants and counting each kind of offspring was produced and analyzed all the data

Parent generation – 1st individuals crossedF1 generation – produced from P generationF2 generation – F1 self-pollinates

Cross Pollinate

Cross-pollinating purple flowers with white produced only purple flowers in the first filial generation.

Producing an F2 Generation

Allowing the F1 generation to self-pollinate, he found that in the secondfilial generation there was about a 3:1 ratio of purple flowers to white.He did hundreds and thousands of crosses

What does this mean?• Before this experiment, people thought offspring had a blend of parents traits• experiment proved this to be false• Offspring show one or the other not a blendOrganisms have 2 factors for each character some factors (traits) are recessive while others are dominant

gene – segment of DNA on a chromosome that controls a particular hereditary trait allele -Two or more alternative forms of a gene (each parent gives one allele for a given trait)

Dominant and Recessive Genes

Dominant genes – genes that keep other genes from showing their traits

Recessive genes – the genes that do not show their traits when dominant genes are present

Genes on the Choromsome

Human LCN6 gene location on chromosome 9q34 A, Ideogram of chromosome 9. Filled triangle near the long arm telomere indicates the location of the lipocalin-rich region containing LCN6. B, Arrangement of lipocalin genes from 126 to 136 megabases from the telomere of the short arm (not to scale). Arrows indicate direction of transcription of each gene. LCN5 and LCN8 indicate uncharacterized genes similar to mouse Lcn5 and 8. Positions were taken from MapView at the The National Center for Biotechnology Information (NCBI) website Human Genome Build 34, Version 1. C, Intron-exon structure of LCN6 gene. Black boxes indicate translated regions and white boxes indicate untranslated regions of exons.

Hamil et al. Reproductive Biology and Endocrinology 2003 1:112 doi:10.1186/1477-7827-1-112http://www.rbej.com/content/1/1/112/figure/F1?highres=y

Law of Segregation

The two alleles separate when the gametes are formed, and only one allele is present in each gamete.

Letters Represent Alleles Geneticists use letters be used to represent

alleles.– A capital letter = Dominant trait– A lowercase letter = a recessive trait– The same letter is used to indicate both alleles

Examples:Flower color: P= purple, p= white Seed color: Y= yellow, y = green Seed shape: R = wrinkled, r = round

Human Traits: tongue rolling ability

Not Rolling = RecessiveRolling = Dominant

Trait: Dimples or No Dimples

Dimples = Dominant No Dimples = Recessive

Curved = RecessiveStraight = Dominant

Trait: Curved Thumb or Straight Thumb

Homozygous

If two alleles of a particular gene present in an individual are the same, the individual is said to be homozygous for that characteristic

AA = homozygous dominantaa = homozygous recessive

Heterozygous

If the alleles of a particular gene present in an individual are different, the individual is heterozygous for that characteristics

Aa = heterozygous

Phenotype

The physical appearance of a characteristic

If the letter A represents the color of a chicken’s feathers and A = brown and a = white, the possible phenotypes for chicken feather are either brown or white

Genotype

The set of alleles (or genes) that an individual has for a characteristic

Chickens could have the genotype AA, Aa, or aa (homozygous dominant, heterozygous, or homozygous recessive) for feather color

Probability

The likelihood that a specific event will occur (usually expressed as a decimal, percentage or a fraction)

Punnett Square

A diagram that biologists use to aid them in predicting the probable distribution of inherited traits in offspring

http://celebritygeckos.com/Portals/28/Genetics/Genetics/basicpunnetsquare.JPG