Do Now 2: Match and explain the following:. Codominance Incomplete Dominance Multiple Alleles Pleiotropy Epistasis Polygenic traits. Exceptions to Mendel’s Rules. Examples. Black, Brown, Yellow Labs Sickle Cell Disease White & Red Flowers make pink flowers Red Blood Type
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Do Now 2: Match and explain the following: • Codominance • Incomplete Dominance • Multiple Alleles • Pleiotropy • Epistasis • Polygenic traits Exceptions to Mendel’s Rules Examples • Black, Brown, Yellow Labs • Sickle Cell Disease • White & Red Flowers make pink flowers • Red Blood Type • Black & White feathers on a rooster
Chromosomes & human Genetics Chapter 09
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 1.) Genes are units of information about heritabletraits. • Genes are located on chromosomes. • Each gene has a specificlocation on a particular chromosome known as the gene’s locus.
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 2.) A cell with a diploid (2n) chromosome number has inherited pairs of homologous chromosomes. • All but one pair of chromosomes (the sex chromosomes) are identical in their length, shape, and gene sequence.
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 3.) Genes at the same loci on homologous chromosomes may be molecularly the same or different. • Although there may be many variation of a particular gene, a diploid cell has only a pair of them. • 4.) The different molecular forms of a gene at a given locus are called alleles. • Alleles arise through mutations.
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 5.) A wild typeallele is the most common form of a gene. • Any less common form of a gene is called a mutant allele.
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 6.) Genes on the same chromosome are physically linked together (thus we call them linked genes). • The farther apart two linked genes are, the more vulnerable they are to crossing over. • Crossing over results in genetic recombination. • Genetic Recombinationresults in nonparental combinations of alleles in gametes, then in offspring.
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 7.) Independent Assortment: Randomalignment of each pair of homologous chromosomes during metaphase I of meiosis. • Results in nonparental combinations of alleles in gametes, then in offspring. • Increasesgenetic variation among a population.
Chromosomal Basis of Inheritance: 8 Things to Remember About chromosomes • 8.) Abnormal occurrences during meiosis or mitosis occasionally change the number & or structure of chromosomes.
2 Basic Types of Chromosomes • Autosomes consist of all chromosomes except sex chromosomes. • Sex chromosomesare types of chromosomes which determine the sex of an individual. • Human sex chromosomes are the X& Y chromosome
Karyotyping (Review) • What are karyotypes and what are they used for? • Karyotypes are an image of chromosomes and their homologous pairs. • Karyotypes are used to observechromosomes by genetic councilors.
Karyotyping (Review) • Remember how to make a karyotype? • Blood sample into a hypotonic solution. • RBC Burst • WBC Swell • WBC frozen during metaphase of Mitosis. • Chromosomes are stained and arranged according to size by a computer program.
Sex Determination in Humans • During meiosis, a woman’s gametes will all receive the _____ sex chromosome. • So each of the woman’s eggs will have the ___ sex chromosome. X X XX X X
Sex Determination in Humans • During meiosis, ½ of a man’s gametes will receive the ___ sex chromosome, and the other ½ the ____ sex chromosome. • So ½ the man’s sperm will have the ___ chromosome, and the other ½ the ___ X Y X Y XY X Y
50/50 shot X Y X X
Sex-Linked Genes • X & Y are not homologous because they do not contain matching genes. • Genes found only in the X-chromosome are X-linked. • Genes found only in the Y-chromosome are Y-linked. • Any gene found on a sex chromosome, X or Y, is sex-linked.
Gene Location • By observing the frequency of crossing over between lined genes, geneticists can create a rough gene map of the given chromosome.
Do Now 3: Part 1. Which Mendelian Exception are each of the following examples: • For a given trait, the phenotype found most frequently in nature is said to be the _______ type and alternative phenotypes are called ______ types. • Explain when, and how crossing over can occur? • What does it mean if a group of genes are linked? • What do we call that group? • Black, Brown, Yellow Labs • Sickle Cell Disease • White & Red Flowers make pink flowers • Red Blood Type • Black & White feathers on a rooster Part 2. Answer the followng
Gene Location 0 • Linked alleles can be separated by crossing over • Recombinant chromosomes are formed • Thomas Hunt Morgan demonstrated this in early experiments • Geneticists measure genetic distance by recombination frequency
Thomas Hunt Morgan realized that the gene for eye color and another gene for wing size are both located on the X chromosome. • Multiple linked genes located on the same chromosome are referred to as a linkage group.
0 b A B A B A b a a B a b Tetrad Crossing over Gametes
Experiment 0 Gray body, long wings (wild type) Black body, vestigial wings GgLl ggll Female Male Offspring Black vestigial Gray vestigial Gray long Black long 944 185 965 206 Parental phenotypes Recombinant phenotypes 391 recombinants 2,300 total offspring = 0.17 or 17% Recombination frequency = Explanation g l G L ggll (male) GgLl (female) g l g l g l g l g L G L G l Sperm Eggs g l g L G L G l g l g l g l g l Offspring
Experiment 0 Gray body, long wings (wild type) Black body, vestigial wings ggll GgLl Male Female Offspring Gray long Black vestigial Gray vestigial Black long 944 206 185 965 Parental phenotypes Recombinant phenotypes 391 recombinants 2,300 total offspring = 0.17 or 17% Recombination frequency =
0 Explanation g l G L GgLl (female) ggll (male) g l g l g l g L g l G L G l Sperm Eggs g l g L G L G l g l g l g l g l Offspring
Geneticists use crossover data to map genes 0 • Genetic maps • Show the order of genes on chromosomes • Arrange genes into linkage groups representing individual chromosomes
Recombination Used as a Map • If 2 linked genes recombine often, they are located far apart. • If 2 linked genes recombine rarely, they are located closer together. • The samples are taken by counting the occurrences of recombination within the offspring.
0 Chromosome l g c 17% 9.5% 9% Recombination frequencies
0 Mutant phenotypes Cinnabar eyes (c) Brown eyes Short aristae Black body (g) Vestigial wings (l) Long aristae (appendages on head) Gray body (G) Normal wings (L) Red eyes Red eyes (C) Wild-type phenotypes
Review • The results of the actual cross are listed below: • 10 Thunderbolt, Yellow, Striped • 9 No thunderbolt, blue, No stripes • 3 Thunderbolt, Yellow, no stripe • 2 No thunderbolt, Yellow Striped • 4 Thunderbolt, Blue, Striped • 4 No thunderbolt, Blue, Striped • 0 Thunderbolt, Blue, No stripe We know that thunderboltattack, color, and stripes are linked in Pikachus. Thunderbold (T) is dominant to no thunderbolt (t) Yellow color (Y) is dominant to blue color (y) Stripes (S) are dominant to no stripes (s). A heterozygous (for all traits) Pikachu mates with a homozygous recessive (for all traits) Pikachu. What is the expected phenotype ratio of the F1 Pikachu generation.
8/30 = 27% 27% 16% 13% Thunder Stripes Color • The results of the actual cross are listed below: • 10 Thunderbolt, Yellow, Striped • 9 No thunderbolt, blue, No stripes • 3 Thunderbolt, Yellow, no stripe • 2 No thunderbolt, Yellow Striped • 4 Thunderbolt, Blue, Striped • 4 No thunderbolt, Blue, Striped • 0 Thunderbolt, Blue, No stripe
Sex-Linked in Humans • Color blindness is an X-linked recessive allele. • What genotype would a colorblind male have? What about a colorblind female? • Which parent passes the colorblind gene to their son? • What would we know about the father of a colorblind girl?
Sex-Linked in Humans X = Noncarrier X = Carries XX XY X X X Y X X X YXX XY
I II Male affected Female Carrier Male Noncarrier Female Noncarrier
Sex-Linked in Humans • Hemophilia is an X-linked disorder. • Results in excessive bleeding due to a lack of clotting chemicals in the blood.
Sex-Linked in Humans • Where will boys receive their X-linked traits from? • Where will girls inherit their X-linked traits from?
Studying human genetics often involves studying family trees and family histories.
Genetic family trees are called pedigrees. A pedigree is a chart that shows how a trait and the genes that control it are inherited within a family (could be family of humans or other organisms).
One carrying a recessive trait that is not expressed is known as a carrier.
I II Male Carrier Female Affected Male Noncarrier
Tay-Sachs Disease • Autosomal (not sex-linked) Recessive • One who is homozygous for Tay-Sachs is not able to break down a certain type of lipid. • This lipid accumulates in the brain eventually causing blindness, brain damage, and eventually death. Those affected rarely live more than a few years.
I II III IV A B A B C D E A B C D E F G H Male Female Carrier Affected Noncarrier A B C D
Cystic fibrosis • Another autosomal recessive allele disorder. • Gene located somewhere on chromosome 7. • Results in an excessive secretion of thick mucus. • This mucus accumulates in the digestive tract and the lungs. • Left untreated, those affected die at a very young age. • With treatment, individuals may make it to young adulthood, and rarely even longer.
Albinism • Results from autosomal recessive alleles. • May result from recessive alleles of many different genes on different chromosomes. • Results in an inability to produce skin pigments. • White Rabbits with pink eyes. • Humans who are homozygous for abinism cannot produce skin pigment melanin. • People with albinism typically have very pale skin and whitish-blond hair.
Dominant Allele Disorders Why would a disorder that is dominant be less likely to be passed on?
Dominant Allele Disorders Disorders that are dominant are rare. The one’s that do exist usually do not manifest or express themselves until after sexual maturity.