2 HeredityPassing of traits from parent to offspring
3 Genetics The study of heredity Gregor Mendel- Austrian monk known as the “father of genetics”
4 Mendel’s Four Hypotheses For each inherited trait, an individual has a copy of that gene from each parent.There are alternate versions of genes, called alleles. (ex: freckles or no freckles)
5 Hypothesis continuedWhen 2 different alleles occur together, one of them may be completely expressed (dominant), while the other may not be observed (recessive).4. Alleles separate independently, so that each gamete only carries 1 allele for that trait.
6 Monohybrid cross Mendel began with 1 trait (monohybrid) crosses He bred pea plants to produce several generationsP- the parent generationF1 - the first filial generationF2 - second filial generation
8 Mendel concluded that each parent has two separate “factors” for a particular trait “Factors” are now called genes.
9 Mendel’s Laws of Heredity Law of Segregation- two alleles separate when gametes are formedLaw of Independent Assortment- alleles of different genes separate independently of one another during gamete formation
10 Mendel’s Law of Segregation Homozygous dominant parentHomozygous recessive parentMendel’s Law of Segregation(chromosomes duplicated before meiosis)meiosis Imeiosis II(gametes)(gametes)fertilization produces heterozygous offspringFig. 11-5, p.172
11 Independent Assortment Nucleus of adiploid (2n)reproductive cellwith two pairs ofhomologouschromosomesPossible alignmentsof the two homologouschromosomes duringmetaphase I of meiosisThe resulting alignmentsat metaphase IIAllelic combinationspossible in gametes1/4 AB1/4 ab1/4 Ab1/4 aBFig. 11-8, p.174
12 Some modern genetic terms Alleles are represented by lettersDominant allele is a capital letterRecessive allele is a lower case letter
13 Homozygous- identical alleles for a specific trait (BB, FF, rr, tt) Heterozygous- alleles are different for a specific trait (Bb, Ff, Rr, Tt) (aka “hybrid”)Genotype- the set of alleles an individual inherits for a trait (i.e.- Rr, Ww, ff)Phenotype- the physical expression of a trait (i.e. blue eyes, freckles, dimples)
14 Punnett Square Predicts possible outcomes of traits Shows all possible outcomes of a genetic cross
15 Probability (likelihood that an event will occur) of a genetic outcome can be predicted Ex: cross two heterozygous individuals Aa x Aapredict ratios of3:1 for phenotype and1:2:1 for genotype
16 PracticeCurly hair is dominant over straight hair. A man with straight hair and a woman who is heterozygous for curly hair have a child. What is the probability that this child will have straight hair?
17 Incomplete Dominance- when an individual shows a combination of the inherited alleles. Ex: red snapdragon x white snapdragon will produce a pink snapdragonstraight hair x curly hair = wavy hair
18 Codominance- 2 dominant alleles are expressed at the same time Ex: Roan horses show both red and white hairs in equal numbers
19 Patterns of heredity can be very complex Sex-linked trait- a trait whose alleles is located on the X chromosome (most are recessive)Polygenic trait- trait where several genes influence the outcome (eye color, hair color, skin color, height, weight)
20 Multiple Alleles- genes with 3 or more alleles - Blood type is an example of multiple alleles because we have A, B and O alleles and 4 possible blood type outcomes(A, B, AB and O)
21 ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii Fig a, p.176
22 DiploidNumber of chromosomes found in the body or somatic cells of an organism“2n”
23 HaploidNumber of chromosomes found in the gametes of an organism“n”
24 Meiosis The type of cell division that produces gametes Gametes = sex cellsfemale gamete = egg or ovum (plural = ova)male gamete = sperm