Chapter 10

Mendel’s Laws of Heredity Who is Gregor Mendel? –Mid 19 th century (1865) –Austrian monk –Loved statistics –Enjoyed gardening –First to apply math to nature

Why did he succeed? Used garden pea –Sexual reproduction (gametes) –Easily pollinated –Self pollinated –Very different and easy to distinguish traits Careful researcher –Studied one trait at a time –Took excellent notes

Monohybrid Crosses Follows ONE trait at a time –P1 generationthe parents –F1 generationthe offspring –F2 generationthe offspring of two F1s Hybrid –The offspring of parents with different traits

Rule of Unit Factors Each organism has two factors (genes) that control each trait There are different forms of these factors (genes) called alleles An organism inherits one allele from the mother and the other from the father +=You!

The Rule of Dominance The trait that is seen in a hybrid cross is dominant The trait that disappears and is not seen in a hybrid cross is recessive A hybrid organism will always look dominant

Law of Segregation Each organism has two alleles for each gene and when gametes are produced, each gamete receives one of these alleles During fertilization, the gametes randomly pair in four different variations

Phenotype vs. Genotype Phenotype: –The way an organism looks –Physical appearance Genotype: –The combinations of genes it has Homozygous- the same alleles Heterozygous- different alleles

Setting up Punnett Squares In rabbits, gray fur is dominant to white fur. Cross a heterozygous gray male with a homozygous white female. X

Practice problems Cross a homozygous gray female rabbit with a white male rabbit Cross a heterozygous female rabbit with a heterozygous gray male rabbit Cross a white male rabbit with a white female rabbit.

Tall pea plants is dominant to short pea plants. Cross a homozygous tall plant with a short plant. Cross a heterozygous pea plant with a homozygous tall plant. Cross a short pea plant with a heterozygous pea plant.

X F1 Genotype F1 Phenotype P1

Dihybrid Crosses Crosses that follow two traits at one time –True breeding –Pure bred –Homozygous Traits are inherited separately

Law of Independent Assortment Genes for different traits are inherited independently from other traits –Seed color is independent from plant height –GgTt creates four different gametes FOIL the gametes First  outside  inside  last

Setting up Dihybrid Crosses X

Phenotypic Ratio What is the probability that it will look a certain way? Genotypic Ratio What is the probability that it will have a certain genetic makeup?

Probability The chance that an event will occur Flip a coin –What is the probability that it will be heads? –The actual outcome is not the same as the probability

Dihybrid Practice Cross a heterozygous tall wrinkled pea plant with a heterozygous tall round pea plant. Cross a homozygous tall round pea plant with a homozygous short round pea plant Cross two heterozygous tall yellow pea plants

Mendel and Meiosis Meiosis is the formation of male and female gametes Occurs only in certain cells –gonads Produces a cell with half the number of chromosomes

Diploid –Having two copies of each chromosome Haploid –Having only one copy of each chromosome Homologous chromosomes –Have the same genetic information –The same gene is located on both

Why meiosis? Provides genetic variation –Can inherit a variety of gene combinations from two parents –With 7 gene pairs you can have 128 possible variations in each parent –Two parents have 16,384 possibilities for offspring Explains the mechanism for Mendel’s Laws

Genetic variation Crossing over –The exchange of genetic material between two homologous chromosomes –Increases the variation Nondisjunction Not-not-joining –When chromatids fail to separate –Resulting gamete has too many or too few chromosomes

Polyploidy –Having more than the usual number of chromosome sets –Makes flowers and fruit larger –Lethal in animals Stawberries Bananas Wheat Chrysanthemums

Darwin’s Ear