Presentation on theme: "Gregor Mendel Gregor Mendel was an Austrian monk who studied genetics and observed how these traits were inherited over several generations. Great."— Presentation transcript:
1 Gregor MendelGregor Mendel was an Austrian monk who studied genetics and observed how these traits were inherited over several generations.Great slide!
2 Gregor MendelHis work was REALLY important to understanding inheritance.He studied what happened when he bred different kinds of pea plants (ex. green vs. yellow, short vs. tall, round vs. wrinkly)From his experiments he came up with several conclusions.Great slide!
3 What did he learn from his studies? Biological inheritance is determined by “factors” (genes within our DNA )that are passed on from one generation to the next.Different forms of these genes determine our physical traits.For every gene, we inherit two alleles (one allele from each parent).Great slide!
4 What did he learn from his studies? trait: specific characteristic that varies from one individual to anotherallele: one of a number of different forms of a genelocus: the location of a gene on a chromosomeGreat slide!
5 Mendel’s three Principles Principle (Law) of Segregationstates that the two different alleles for a gene segregate independenty from one another during meiosisGreat slide!
6 Mendel’s three Principles Principle (Law) of Independent Assortmentstates that different traits sort and are inherited independently of one another when sex cells are formedGreat slide!
7 Mendel’s Principles (A Summary) For every gene, we inherit two copies (one allele from each parent)Blonde HairBrown EyesGreat slide!Blonde HairBlue EyesBrown HairBrown Eyes
8 If we have two sets of manuals, how do we know which directions to follow? If we have two alleles for every trait, how does our body pick which one to express?Blonde HairBrown EyesGreat slide!Blonde HairBlue EyesBrown HairBrown Eyes
9 if we have two sets of manuals, how do we know which directions to follow? When we get directions from each parent, it is a combination of the different directions that determine our traits.Great slide!
10 Mendel’s three Principles Principle (Law) of Dominancestates that when two or more forms of a gene (alleles) exist for a single trait, some alleles are dominant while others are recessiveGreat slide!
11 Principle of Dominance Some alleles are dominant and others are recessive .Organisms with a dominant allele for a particular trait WILL exhibit that trait, because the dominant allele overpowers the recessive allele.Great slide!
12 Principle of Dominance A recessive trait will only show in in the organism when BOTH alleles are recessive – that is, when the dominant allele is NOT present.Great slide!
13 PUNNETT SQUARESA Punnett square is a useful tool used to determine or predict the probability that offspring will have certain traits after a genetic cross.Great slide!
14 PUNNETT SQUARES: probability Probability: the likelihood that a particular event will occurBecause each organism has two alleles for each gene there is an equal (50/50) chance of giving either allele to an offspringGreat slide!
15 PUNNETT SQUARES: terms Genotype: genetic makeup of an organism (alleles)Genotype sounds like genesPhenotype: physical characteristics/appearance of an organismPhenotype sounds like physicalGreat slide!
16 PUNNETT SQUARES: terms Homozygous: an organism with two identical alleles for a particular traitHeterozygous: an organism with two different alleles for the same traitGreat slide!
17 Let’s use those words in an Example Homozygous for the tall trait – “TT” is the genotype, “tall” is the phenotypeHeterozygous for the tall trait – “Tt” is the genotype, “tall” is the phenotypeHomozygous for the short trait – “tt” is the genotype, “short” is the phenotypeGreat slide!
18 PUNNETT SQUARES: Rules Use letters to stand for allelesDominant alleles are noted with a CAPITAL ( D ) letterRecessive alleles for the same trait are noted with the lowercase ( d ) of the same letter.Great slide!
19 PUNNETT SQUARES: Rules Parental genotypes are shown along the top and side of the Punnett square.Write one parent’s alleles on the top, and write the other on the sidePut one letter next to each cell, and drag alleles across or down so that there are two alleles in each square.Great slide!
20 PUNNETT SQUARES: Rules Each of the four squares represents a possible genotype of the offspringThese are just probabilities!Great slide!
21 Punnett square practice 1. A homozygous tall (TT) pea plant is crossed with a homozygous short (tt) pea plant:Great slide!
22 Punnett square practice A homozygous red (RR) flower is crossed with a heterozygous red (Rr) flower:Great slide!
23 Punnett square practice A heterozygous funny (Ff) bird is crossed with a heterozygous funny (Ff) bird:Great slide!
24 Offspring Ratios When you have two homozygous parents? Genotype Ratio: ________ Phenotype Ratio:________When you have one homozygous and one heterozygous parent?When you have two heterozygous parents?Great slide!
25 Multiple generationsSometimes, we need to do a Punnett square to follow more than one generation.Generations: P F1 F parents first filial second filialgeneration generationGreat slide!
26 Test crossesIf you need to figure out the genotype of a parent with the dominant trait, you can do a test cross.This is done by crossing that parent with a homozygous recessive organism.Great slide!
27 Test crossesIf any offspring show the recessive allele, you know that the dominant parent is heterozygous.Great slide!
28 Test crossesIf none of the offspring show the recessive allele, you know that the dominant parent is homozygous.Great slide!
29 Example:A man with free earlobes wants to know if he is homozygous or heterozygous for that trait. He marries a woman with attached earlobes (the recessive trait). His first child has attached earlobes. The man has thus found out that he is _________________________.
30 Going Beyond Dominant and Recessive Alleles Some alleles are neither dominant nor recessive – many traits are controlled by more than one allele or by multiple genes…Great slide!
31 Incomplete dominanceIncomplete dominance: a situation in which one allele is not completely dominant over anotherBecause neither trait dominates the other, sometimes the alleles are written differently (ex. RW, CrCw, DD’)Examples are: flowers (red/pink/white), hair (curly/wavy/straight), fur (long/short)Great slide!
32 Identifying Incomplete dominance Notice that the offspring show a third phenotype that is different from the parentsThe offspring phenotype is a MIX or BLEND of the parental traitsGreat slide!
33 Identifying Incomplete dominance What happens when we cross a red (RR) flower with a white (WW) flower?The offspring look pinkGreat slide!
34 codominancecodominance: a situation in which both alleles of a gene contribute to the phenotype of the organismWhat does the prefix “co-“ mean? to shareBecause neither trait dominates the other, sometimes the alleles are written differently (ex. RW, CrCw, DD’)Examples are: cows (red/roan/white), flowers (red/spotted/white), blood type (A/AB/B)Great slide!
35 Identifying codominance Notice that the offspring show a third phenotype that is different from the parentsThe offspring phenotype has both parental traits appearing TOGETHERGreat slide!
36 Identifying codominance What happens when we cross a pure red (RR) cow with a pure white (WW) cow?The offspring look roan - spotted with red & whiteGreat slide!
37 Identifying codominance What happens when we cross a pure red (RR) cow with a pure white (WW) cow?The offspring look roan - spotted with red & whiteGreat slide!
38 Polygenic traitsTraits controlled by two or more genes are said to be polygenic.Polygenic traits show a wide range of phenotypes because different combinations of alleles on these genes produce many different traits.Great slide!
39 Polygenic traitsFor example, hair color and eye color are controlled by more than one gene and therefore have more than two phenotypes.Great slide!
40 Polygenic traitsAnd, the wide range of skin color in humans is due to more than four different genes that control this trait.Great slide!