Chapter 9 - Introduction to Genetics Genetics – the branch of Biology that studies heredity – how traits are passed on.

Chromosomes Humans have 46 chromosomes arranged in 23 pairs (44 autosomes and 2 sex chromosomes) Chromosomes are made up of DNA and Proteins Chromosomes and therefore the DNA can be divided into genes Genes are short segments of DNA

Chromosome with genes

Karyotype-a picture of chromosomes

Allele – alternate form of a gene Example: Brown/blue, tall/short can be represented by a letter Example: Brown – B Blue - b

Homologous Chromosomes Determines eye color Genes Determines hair color

Brown Allele Blue Alleles Blue Allele b b b B One pair of your chromosomes for eye color One pair of your chromosomes for eye color

Brown Allele Blue alleles Blue Allele b b b B Homozygous – alleles are the same Heterozygous – alleles are different

Homozygous (pure) The two alleles are the same The two letters are the same BB or bb Homozygous Dominant – BB Homozygous Recessive - bb

Heterozygous (hybrid) The two alleles are different The two letters are different Bb

Dominant Gene A gene that will be expressed if it is present Examples – brown, tall, green, purple Written as a capital letter

Recessive Gene A gene that will only be expressed if there are two alleles present Recessive genes are not expressed if there is a dominant gene present Short, blue, yellow, white Written as a lower case letter

Genotype The two alleles an organism has What the genes “say” Ex. BB, Bb, bb

Phenotype Physical appearance of an organism The result of the expression of the genes Example: tall, short, brown, blue

The Goal The goal of genetics is to determine the possible offspring that can be produced from two parents The likelihood of an outcome is determined through the laws of probability

Probability The likelihood that a specific event will occur Can be expressed as a decimal, percent or a fraction

Equation for Probability Number of times an event is expected to happen Probability = The number of opportunities for an event to happen

Probability Example You flip a coin once The probability of getting tails is ½ You flip a coin twice The probability of getting tails twice is 1/4 1 1 1 = X 4 2 2

T H or First Flip Second Flip If I got Tails on the first flip I can either get heads or tails On the second flip H T

Second Probability of getting: First H 1/4 H T 1/4 H 1/4 T T 1/4

Gametes Egg or sperm Haploid Contains half the number of chromosomes One gene from each homologous pair

Early Ideas on Heredity Until the 19th century it was thought that the reason people look like their parents is because they were a blend of both parents. The work of Gregor Mendel changed the views of how characteristics are passed on from 1 generation to the next.

Gregor Mendel Born in 1822 in Austria Studied at the University of Vienna Became a priest and lived in a monastery He was in charge of the garden and he studied pea plants

Gregor Mendel Pea flowers have both male and female parts They normally produce seeds through self-pollination The pollen from the male flower part fertilizes the egg from the female flower part of the same flower These seeds would inherit all their characteristics from the single plant that bore them

Gregor Mendel Mendel figured out that self-pollination could be prevented He cut the male parts off of 1 plant and the female parts off another plant Then he pollinated the 2 plants by dusting the pollen from one onto the flower of the other This is known as cross-pollination Produces seeds with the characteristics of both plants

Gregor Mendel Mendel had a stock of peas that were purebred They would only produce offspring that were identical to them He decided to cross plants with different characteristics to produce hybrids He studied a few isolated characteristics to simplify his experiments

Cross pollination

Gregor Mendel Pea Traits Studied Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled White Constricted Terminal Short

Genetic Crosses When doing genetic crosses it is important to keep tract of the generations P1 – parents F1 – children of the parents (P1) F2 – Children of the F1’s

GG gg Gg gg GG Gg

A Genetic Cross Punnett Square – used to predict the possible outcomes of a cross

AA aa aa Male produces one type of sperm with the gene A                   Male produces one type of sperm with the gene A Female produces one type of egg with the gene a

The Baby Elephants will be.. Aa Aa Aa Aa

Monohybrid Cross a a Aa A A

How to fill in the Punnett Square

Monohybrid Cross Cross where one trait is looked at Dark elephant vs. light elephant

Aa Aa Male produces two Female produces two types of sperm with                   Male produces two types of sperm with the gene A or a Female produces two type of eggs with the gene A or a

The Baby Elephants will be.. Aa AA aa Aa

Genotypic Ratio Ratio of the offspring's genotypes Genotypic Ratio: 1:2:1 EE – 1 Ee – 2 ee – 1

Phenotypic Ratio Ratio of the offspring's phenotypes Phenotypic ratio: 3:1 3 – smooth 1- wrinkled

Phenotypes? Genotypic Ratio? Genotypes? Phenotypic Ratio?

Law of Segregation A pair of genes is segregated or separated during the formation of gametes

Law of Independent Assortment Genes for different characteristics are not connected They are inherited independently

Dihybrid Cross A cross between individuals that involves two pairs of contrasting traits Look at hair color and eye color at the same time Look at height and color at the same time

Dihybrid Cross Punnett Square

AABB aabb AB ab ab AB AB AB ab ab

Sperm Egg AB ab Fertilization AB ab AaBb Genes in the fertilized egg

Dihybrid Cross Two traits are crossed at the same time Color and height A=tall a=short B=Yellow b=white AaBb x AaBb

B AB A b Ab aB B b ab a How to find genes for the gametes of a dihybrid cross B AB A b Ab aB B a b ab

ab ab ab ab AaBb AB AB AB AB

AaBb Genotypic Ratio: 1 Phenotypic Ratio: 1

What if the Dihybrid cross has heterozygous parents? How do you find the gametes?

AaBb AaBb AB AB Ab Ab aB ab aB ab

B=black b=brown S=Short hair S=long hair

Dihybrid Heterozygous Cross Genotypic Ratio 1:2:1:2:4:2:1:2:1

Testcross When an individual of unknown genotype is crosses with a homozygous recessive individual B? x bb

The End