2 23.1 Mendel’s Laws Gregor Mendel Investigated inheritance at the organism level (1860’s)Concluded that plants transmit distinct factors to offspringBased on his studies, he formulated the law of segregation
3 23.1 Mendel’s Laws The Law of Segregation Each individual has two factors for each traitThe factors segregate (separate) during the formation of gametesEach gamete contains only one factor from each pair of factorsFertilization gives each new individual two factors for each trait
4 23.1 Mendel’s LawsToday we know genes determine characteristics of an organism, genes are found on chromosomesChromosomes that are homologous are members of a pair and carry genes for the same traits in the same orderAlleles are alternate forms of a gene for the same traitAlleles are always at the same locus (location) on each chromosome of a homologous pair
6 23.1 Mendel’s Laws The Inheritance of a Single Trait Phenotype: physical appearance of the individual with regard to a traitGenotype: Alleles responsible for a given traitTwo alleles for a traitA capital letter symbolizes a dominant allele (W)A lower-case letter symbolizes a recessive allele (w)Dominant refers to the allele that will mask the expressionof the alternate (recessive) allele
8 23.1 Mendel’s Laws Gamete Formation During meiosis, homologous chromosomes separate so there is only 1 member of each pair in a gameteThere is one allele for each trait, such as hairline, in each gameteNo two letters in a gamete can be the same letter of the alphabetIf genotype is Ww, then gametes from this individual will contain either a W or a w
9 23.1 Mendel’s Laws One-Trait Cross A homozygous man with a widow’s peak(X)A woman with a straight hairline
10 23.1 Mendel’s Laws One-Trait Cross Two individuals who are both Ww A Punnett Square is useful to solve this problem
11 23.1 Mendel’s Laws One-Trait Crosses and Probability The chance of 2 or more independent events occurring together is the product of their chance of occurring separatelyIn the cross Ww X Ww, what is the chance of obtaining either a W or a w from a parent?Chance of W = ½ and the chance of w = ½Therefore the probability of having these genotypes is as followsChance of WW= ½ X ½ = ¼Chance of Ww = ½ X ½ = ¼Chance of wW= ½ X ½ = ¼Chance of ww = ½ X ½ = ¼
12 23.1 Mendel’s Laws The One-Trait Test Cross Breeders of plants and animals may do a test cross to determine the likely genotype of an individual with the dominant phenotypeCross with a recessive individual-has a known genotypeIf there are any offspring produced with the recessive phenotype, then the dominant parent must be heterozygous
14 23.1 Mendel’s Laws Practice Problems Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles?
15 23.1 Mendel’s Laws Practice Problems Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents?
16 23.1 Mendel’s Laws Practice Problems A father has dimples, the mother of his children does not, and all 5 of their children have dimples. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all persons concerned.
17 23.1 Mendel’s Laws The Inheritance of Two Traits The Law of Independent Assortment:Each pair of factors assorts independently (without regard to how the others separate)All possible combinations of factors can occur in the gametes
20 23.1 Mendel’s Laws Two-Trait Crosses (Dihybrid Cross) WwSs (X) WwSs Phenotypic Ratio:9 widow’s peak, short fingers3 widow’s peak, long fingers3 straight hairline, short fingers1 straight hairline, long fingers
21 23.1 Mendel’s Laws Two-Trait Crosses and Probability Probability Laws Probability of widow’s peak = ¾Probability of short fingers= ¾Probability of straight hairline= ¼Probability of long fingers= ¼Using the Product RuleProbability of widow’s peak and short fingers = ¾ X ¾ = 9/16Probability of widow’s peak and long fingers = ¾ X ¼ = 3/16Probability of straight hairline and short fingers = ¼ X ¾ = 3/16Probability of straight hairline and long fingers = ¼ X ¼ = 1/16
22 23.1 Mendel’s Laws Practice Problems Attached earlobes are recessive, What genotype do children have if one parent is homozygous recessive for earlobes and homozygous dominant for hairline, and the other is homozygous dominant for unattached earlobes and homozygous recessive for hairline?
23 23.1 Mendel’s Laws Practice Problems If an individual from this cross reproduces with another of the same genotype, what are the chances that they will have a child with a straight hairline and attached earlobes?
24 23.1 Mendel’s Laws Practice Problems A child who does not have dimples or freckles is born to a man who has dimples and freckles (both dominant) and a woman who does not. What are the genotypes of all persons concerned?
25 23.1 Mendel’s Laws Pedigrees A chart of family’s history with regard to a particular genetic traitMales =Females =Affected individuals (for a given trait) are shaded
27 23.2 Beyond Simple Inheritance Patterns Incomplete DominanceOccurs when the heterozygote is intermediate between the two homozygotesCodominanceOccurs when alleles are equally expressed in a heterozygoteBlood type AB is an exampleRed blood cells have both Type A and Type B surface antigens
29 23.2 Beyond Simple Inheritance Patterns Multiple Allele InheritanceA trait is controlled by multiple alleles, the gene exists in several allelic forms.Each person has only two of the possible alleles.
30 23.2 Beyond Simple Inheritance Patterns Multiple Allele InheritanceABO Blood TypesIA = A antigens on red blood cellsIB = B antigens on red blood cellsi = has neither A nor B antigens on red blood cellsBoth IA and IB are dominant over i, IA and IB are codominantPhenotype GenotypeA IAIA or IAiB IBIB or IBiAB IAIBO ii
31 23.2 Beyond Simple Inheritance Patterns Multiple Allele InheritanceABO Blood TypesBoth IA and IB are dominant over i, IA and IB are codominantThe Rh factor is inherited separately from ABO blood types.
33 23.2 Beyond Simple Inheritance Patterns Practice ProblemsIf a person with straight hair marries someone with wavy hair, can they have a child with curly hair?
34 23.2 Beyond Simple Inheritance Patterns Practice ProblemsA child with type O blood is born to a mother with type A blood. What is the genotype of the child? The mother? What are the possible genotypes of the father?
35 23.2 Beyond Simple Inheritance Patterns Practice ProblemsFrom the following blood types determine which baby belongs to which parents:Baby 1 type O Mrs. Doe type A Mrs. Jones type ABaby 2 type B Mr. Doe type A Mr. Jones type AB
36 23.2 Beyond Simple Inheritance Patterns Sex-Linked InheritanceIn Humans:22 pairs of autosomes, 1 pair of sex chromosomesX and YIn females, the sex chromosomes are XXIn males, the sex chromosomes are XYNote that in males the sex chromosomes are not homologousTraits controlled by genes in the sex chromosomes are called sex-linked traitsX chromosome has many genes, the Y chromosome does not
37 23.2 Beyond Simple Inheritance Patterns Sex-Linked AllelesRed-green colorblindness is X-linkedThe X chromosome has genes for normal color visionXB = normal visionXb – colorblindnessGenotypes PhenotypesXBXB female with normal color visionXBXb carrier female with normal color visionXbXb colorblind femaleXBY male with normal color visionXbY colorblind male
39 23.2 Beyond Simple Inheritance Patterns Practice ProblemsBoth the mother and the father of a colorblind male appear to be normal. From whom did the son inherit the allele for colorblindness? What are the genotypes of the mother, father, and the son?
40 23.2 Beyond Simple Inheritance Patterns Practice ProblemsA woman is colorblind. What are the chances that her son will be colorblind? If she is married to a man with normal vision, what are the chances that her daughters will be colorblind? Will be carriers?
41 23.2 Beyond Simple Inheritance Patterns Practice ProblemsA husband and the wife both have normal vision. The wife gives birth to a colorblind daughter. Is it more likely the father had normal vision or was colorblind? What does this lead you to deduce about the girl’s parentage?
42 23.2 Beyond Simple Inheritance Patterns Polygenic InheritanceOccurs when a trait is governed by two or more sets of alleles.Each dominant allele codes for a productThe effects of the dominant alleles are additive.The result is continuous variation.Examples of traits include size or height, shape, weight, and skin color.
44 23.2 Beyond Simple Inheritance Patterns Practice ProblemsA certain polygenic trait is controlled by three pairs of alleles: A vs a, B vs b, and C vs c.What are the extreme genotypes for this trait?
45 23.3 Environmental Influences Environmental factors can influence the expression of genetic traits.Examples:Primrose flowers are white at warmer temperatures and red at cooler temperaturesSiamese cats and Himalayan rabbits are darker in color where body heat is lost to the environment.
47 23.4 Inheritance of Linked Genes All the alleles on one chromosome form a linkage group.Recall that during meiosis crossing over sometimes occursIf crossing over occurs between two alleles of interest, then four types of gametes are formed instead of two
49 23.4 Inheritance of Linked Genes The occurrence of crossing-over can help determine the sequence of genes on a chromosomeCrossing-over occurs more often between distant genes than genes that are close togetherIn the example below, it is expected that recombinant gametes would include G and z more often than R and s.
50 23.4 Inheritance of Linked Genes Practice ProblemsWhen AaBb individuals reproduce, the phenotypic ratio is about 3:1. What ratio was expected? What may have caused the observed ratio?
51 23.4 Inheritance of Linked Genes Practice ProblemsThe genes for ABO blood type and for fingernails are on the same homologous pair of chromosomes. In an actual family, 45% of offspring have type B blood and no fingernails, and 45% have type O blood and fingernails; 5% have type B blood and fingernails, and 5% have type O blood and no fingernails. What process accounts for the recombinant phenotypes?