Presentation on theme: "Gregor Mendel “Father of Genetics” Wrote “Experiments in Plant Hybridization” in 1865 His work wasn’t discovered until the next century."— Presentation transcript:
Gregor Mendel “Father of Genetics” Wrote “Experiments in Plant Hybridization” in 1865 His work wasn’t discovered until the next century
Painting of Mendel
Table 14.1 The Results of Mendel’s F 1 Crosses for Seven Characters in Pea Plants
Sweet Pea Flowers
Alleles, Alternative Versions of a Gene
Homozygous means having only one form of gene or allele Ex: WW or ww
Heterozygous means a trait represented by at least two different alleles, or forms of a gene Ex: Ww
In the formation of a zygote, or fertilized egg, each parent of an organism contributes one form of a gene or allele, for each trait in most cases.
In Mendelian Genetics, dominant traits are represented by capital letters; recessive ones by lower case letters
Dominant traits (genes) are always expressed if the gene is present; recessive traits are expressed only if the dominant genes are absent
For example, widow’s peak (W) is a dominant trait in humans. If the gene for widow’s peak is present, W, the person will have widow’s Peak. (WW, Ww)
Homologous Chromosomes eye color locus b = blue eyes eye color locus B = brown eyes Paternal Maternal This person would have brown eyes (Bb)
Meiosis - eye color Bb diploid (2n) B b meiosis I B B b b sperm haploid (n) meiosis II
The physical appearance of an organism is known as the phenotype; the genetic makeup (the letters) are known as the genotype Ex: Widow’s peak is the pheno- type; Ww is the genotype
The way to show the pos- sible pairings of genes between two organisms is called a Punnett Square.
Punnett Square Punnett square combinations gametesA Punnett square is used to show the possible combinations of gametes.
P generation Breed the P generation tall (TT) vs. dwarf (tt) pea plantstall (TT) vs. dwarf (tt) pea plants t t TT
tall (TT) vs. dwarf (tt) pea plants t t TT Tt All Tt = tall (heterozygous tall) produces the F 1 generation
F1 generation Breed the F1 generation Heterozygous Tall (Tt) pea plantsHeterozygous Tall (Tt) pea plants T t T t
Cross a purebred black guinea pig and a purebred brown guinea pig. Black is dominant over brown.
B b b Bb (black) (Brown) All offspring are black and heterozy gous.
If bushy eyebrows (B) are dominant over fine eyebrows, (b), show the cross between one parent heterozygous for the trait and one who is homozygous recessive.
What are the phenotypes and genotypes of the offspring? Answer: Bushy (Bb) 50% and fine (bb) 50%
Monohybrid Cross single trait.A breeding experiment that tracks the inheritance of a single trait. Dihybrid Cross A breeding experiment that tracks two traits. the inheritance of two traits.
Mendel’s “principle of segregation” a. pairs of genes on homologous chromosomes separate gamete (meiosis) during gamete formation (meiosis) and end up in different gametes. gametes b.the fusion of gametes at fertilization pairs genes once again. Ex: The alleles for height in Mendel’s pea plants end up in separate gametes. Tt X Tt could yield four the offspring: TT, Tt, Tt, tt.
Meiosis - eye color Bb diploid (2n) B b meiosis I B B b b sperm haploid (n) meiosis II
Mendel’s Law of Segregation
Mendel’s “principle of independent assortment” (2 different genes)Mendel’s “principle of independent assortment” (2 different genes) a.each pair of alleles on nonhomologous chromosomes segregates independently of other pairs during gamete formation Ex: When Mendel crossed F1 plants that were heterozygous for round yellow peas, some F2 plants did not resemble the parent plants.
Independent Assortment How many different gametes can be produced for the following allele arrangements? 2 n (n = # of heterozygotes)Remember: 2 n (n = # of heterozygotes) 1.RrYy 2.AaBbCCDd 3.MmNnOoPPQQRrssTtUu
Answers: 1. RrYy: 2 n = 2 2 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2 n = 2 3 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtUu: 2 n = 2 6 = 64 gametes
Autosomal Inherited Traits are inherited via the autosomes (non-sex) chromosomes. How many autosomes are in each of your somatic cells?
That’s right! There are 44 autosomes and 2 sex chro- mosomes in each of your somatic (non-sex) cells.
Figure 13.x5 Human male karyotype shown by bright field G-banding of chromosomes
Autosomal Inherited Genetic Disorders include: Cystic Fibrosis Tay-Sachs Disease Sickle Cell Anemia Huntington Disease (this one is dominant!)
Testing a Fetus for Genetic Disorders
Cystic Fibrosis Most common inherited fatal disorder in the U.S. Median age of death–37 One in every 29 Americans has the gene Mucus builds up in the lungs
Francis Collins, current director of the National Human Genome Research Institute (NHGRI) helped pioneer the discovery of the CF gene in 1989.
Francis Collins, discoverer of the Cystic Fibrosis Gene
Former NFL Quarterback, Boomer Esiason and his son, Gunnar, who has CF.
If a man who does not have Cystic Fibrosis has a sister who died of CF. He marries a woman who does not have the disease or any history of it in her family, what is the probability that they will have kids with the disease?
Tay Sachs Disease a lipid-digesting enzyme is defective in lysosomes
If two parents are each carriers of the gene for Tay-Sachs Disease, what is the probability of them having a child with the disease?
That’s right! They have a 25% chance! T t T t TT Tt tt Homozygous Dominant Heterozygous Homozygous Recessive
Sickle Cell Anemia
The molecular basis of sickle-cell disease: a point mutation
Huntington Disease A degenerative disorder of the nervous system Most people don’t realize that they have the disease until after age 30 and may have passed on the gene
Lake Maracaibo, Venezuela
Nancy Wexler’s Pedigree of 10,000 people in Lake Maracaibo
Huntington Disease (chorea)
Caused by a stuttering gene - CAG repeat Also called Huntington’s Chorea This is a dominant gene
Some human traits are sex-linked; that is they are carried on the X and Y Chromosomes
For Example: Hemophilia, Duchenne Muscular Dystrophy, and Colorblindness are all traits carried on the X chromo- some
Duchenne Muscular Dystrophy
If a female who is carrier for Duchenne Muscular Dystrophy (D), what is the probability of she and her“normal”husband having a child with MD?
X Y D X D D d X D d X Y D d Male with Disease Carrier Female Normal
A pedigree shows the genetic relationship between organisms or people.
Bloodtypes are also inherited: A = has antigen A B = has antigen B O =neither AB =has both antigens A and B
Genotypes O = OO AB = AB A = AA or AO (codominance) B = BB or BO (codominance)
Alleles and Genes Interact to Produce Phenotypes Codominance—two alleles of a gene produce phenotypes that are both present in the heterozygote. Example: ABO blood group system has three alleles of the gene: I A, I B, and I O.
ABO Blood Reactions Are Important in Transfusions
O is the universal donor (can donate blood to anyone) AB is the universal recipient ( can receive blood from anyone)
PatientDonor AA or O BB or O AB anyone O a person who is Rh negative for any blood type must take only Rh negative blood
The Rh Factor is also inherited. Approximately 85% of Americans are positive for the Rh Factor. For example, if you have type A blood and are positive for the Rh Factor then your bloodtype is A positive.
So technically there are 8 blood groups: A positiveAB positive A negativeAB negative B positive O positive B negative O negative
In terms of a couple having kids, positive blood dominates negative blood. For example, a father with A positive blood and his wife with A negative blood would have kids with A positive blood.
RhoGAM A woman who is pregnant and is Rh negative and has an Rh positive child must take RhoGAM in order to not reject the child.
If a woman who is type O and a man who is type A have kids, what are their possible bloodtypes?
O A A AO WOMAN MAN
A O O O OO AO OO
1) If a brown eyed man marries a brown eyed woman and they have a blue eyed child, what are the genotypes of the parents?
2) In rabbits, the allele for black coat color (B) is dominant over the allele for brown coat color (b). Predict the results of a cross between a rabbit homozygous for black coat color (BB) and a rabbit homozygous for brown coat color (bb)
3) If two sisters in a family have free earlobes (F) and their two brothers have attached earlobes (f), what genotypes are the parents most likely to have if neither parent has attached earlobes?
4) What is the probability of a couple who are both heterozygous for widow’s peak (W) and free earlobes (F) having a child with neither trait?
5) In pea plants, smooth seed texture is dominant over wrinkled seed texture. A gardener has a pea plant that produces smooth seeds. How can the gardener determine whether the plant is homozygous or heterozygous for the allele that determines seed texture?
6) In pea plants, if purple flowers are dominant over white, and smooth seeds are dominant over wrinkled, predict the out- come of the crossing of a pea plant heterozygous for color and homozygous recessive for seed coat texture with one heterozygous for both traits.
7) In fruit flies, L = long wings and l = short wings. When a long-winged fly is crossed with a short-winged fly, the offspring exhibit a 1:1 ratio. What is the genotype of the parent flies?
8) In squash an allele for white color (W) is dominant over yellow (w). Give the phenotypic ratios for the results of each of the following crosses: a) W/W x w/w b) W/w x w/w c) W/w x W/w
9) In humans, pointed eyebrows (B) are dominant over smooth eyebrows (b). Mary’s father has pointed eyebrows, but she and her mother have smooth. What is the genotype of the father?
10) In tomatoes, red fruit (R) is dominantover yellow fruit (r), and tallness (T) is dominant over shortness (t). A plant that is RrTT is crossed with aplant that is rrTt. What are the chances of an offspring beingheterozygous for both traits?
11) In fruit flies, gray wings (G) are dominant to black wings and normal wing length (N) is dominant to vestigial (short) wing length. What is the probability of a gray fly with normal wings heterozygous for both traits and a black fly with normal wings, but homozygous for wing length having offspring which are gray and have normal wing lengths?
12) Free ear lobes (F) and widow’s peak (W) are dominant traits in humans. What is the probability of a woman who has attached earlobes and no widow’s peak and a man who is heterozygous for both traits having kids who have attached ear lobes and no widow’s peak?
Genes A and B are 6 map units apart, and A and C are 4 map units apart. Which gene is in the middle if B and C are 10 map units apart? Which is in the middle if B and C are 2 map units apart?
In the cross RrTt X rrtt, a. all of the offspring will be tall with red fruit b. 75% will be tall with red fruit c. 50% will be tall with red fruit d. 25% will be tall with red fruit
In terms of evolution, why is the incidence of sickle cell anemia higher among the African-American population in the United States?
If one parent has type O blood and one of the kids is type A, what are the possible blood types of the other parent? If one parent has type AB blood and the other has A, what are the possible blood types of the kids?
For most human traits, how many alleles does each parent contribute to the zygote or fertilized egg? What is the term used to describe traits that are inherited by a number of genes of each parent?
If you have good notes from yesterday on Cystic Fibrosis you should be able to: 1)describe at least two organs affected 2)show a Punnett square with the inheritance pattern 3) list one organization which raises awareness of CF 4) name and describe the specific protein affected by CF 5) significance of discovery of the CF gene
When RhoGAM is given to a pregnant mother, what is the Rh status of the mother, father, and baby?