Chromosomes…What are the two types? • Sex chromosomes and Autosomes • Sex chromosomes determine? • Autosomes code for? • MALE genotype? FEMALE?
Sex Determination—how’s it work? • Chance of sperm getting X or Y? • Chance of an egg getting a Y? • Chance of egg getting X? • What’s SRY? • Sex-determining Region Y (gene)..Which means? SRY = gonad develops as testes No SRY = ovaries
Sex Determination Male or Female?
Brain Break!Don’t Forget...Family Surveys! • Due When? • How many? • Who at minimum???
2 Types of Mutations Germ Cell Somatic Cell
Deletion Inversion Translocation Nondisjunction Point Mutation Substitution Frameshift Mutation Insertion Mutation
Chromosomal Mutations Deletion Inversion Translocation Nondisjunction http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60215.htm
Point Mutation Frameshift Mutation Insertion Mutation Substitution Gene Mutations http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60216.htm
Effects of Gene Location • Morgan’s fruit fly eye-color experiments • Where is the eye-color gene located? • XRXR x XRY • XRXr x XRY • WHAT’s this called???
Sex-linked Genes and Traits • Sex-linked trait: • Coded for by allele on sex chromosome (X, Y) • Is SRY sex-linked? • Duchenne Muscular Dystrophy, Hemophilia, red/green colorblindness
Duchenne muscular dystrophy • Gene translation: defective muscle protein • Lethal, young adults • 1:3000 males in US
Colorblindness • Inability to distinguish certain colors • Red-Green-- • 1:10 males in US; 1:100 females
Hemophilia • Gene that codes for blood clotting protein • 1:1000 males
Y X So, WHY are more Males Affected?!?!?!?!? • Female (#23)Genotype: • Male Genotype: • Punnett Square: Normal Dad x Carrier Mom • Females : carriers (heterozygotes) or AA or aa • Males only get one X, so if it’s got the bad (recessive) allele, they’re affected
Y X Females can carry sex-linked genetic disorders but males can’t! • Males (XY) express all of their X-linked genes. • WHY????? • SO NO MALE HETEROZYGOTES!
If mom’s a carrier of an X-linked recessive disorder and dad’s normal, what’s the probability that they’ll have a normal child?
If dad’s got an X-linked recessive disorder and mom’s normal (not a carrier), what’s the probability that they’ll have a normal child?
And this... It is estimated that we all carry between six and nine lethal recessive genes. Assume you are all carrying (heterozygous) the recessive disorders in Table 2. Assign your genes to the appropriate chromosome as done earlier
Linked Genes • Same as sex-linked genes? • Pairs of genes that tend to inherit together • On fruit flies: eye color and wing length
How the heck do they figure this out?! • http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60211.htm
What’s a pedigree diagram? • Shows inheritance of a trait over several generations • Horizontal lines • Vertical lines • Circles • Square • Colored/not colored • Roman #s • Left to right
Tracing genes in families!! Remember this? Phenotypes used to infer genotypes!!
Inheritance of Traits • If autosomal inheritance: • In both sexes equally • Recessive disorders: affected must be hom rec!
Pedigree Male Female Has trait No trait How do you show a carrier????
Inheritance of Traits • If sex-linked inheritance: • More males than females • Females carriers
Sex-Linked? Dominant or Recessive? The gene for this particular genetic trait does not occur on the sex chromosomes; it occurs on an autosomal chromosome because both males and females have the trait. This information can be inferred from two facts: (1) Because the father has the trait, if the trait were sex-linked (on the father’s X chromosome), then all females would have the trait. However, because some females do not have the trait, it is not a sex-linked trait. (2) Individual III-7 who (male) didn’t inherit the trait from his mom, who has the trait. He received his only X chromosome from his mother. This particular gene is a dominant gene because ○ each of the people who have the trait has only one parent who has the trait. ○ if only one parent has the trait and the trait is not sex-linked, then the individuals who have the trait must be heterozygous for the gene.
Look at your family history surveys DRAW on the sheet… Arrange them with Grandparents = GENERATION I Parents = GENERATION II You, siblings = GENERATION III Make connection lines for marriages, etc. HIGHLIGHT ONE TRAIT…asthma, etc. Complete the questions! YOUR FAMILY PEDIGREE
Genetic Disorders • Diseases or disabling traits inherited genetically • Complex characters: • Environmental factors influence trait also • Skin color • Breast cancer, diabetes, heart disease, stroke, schizophrenia
Example of environmental influences? The same flower Grown in different pH soils Basic Acidic Smoking, exposure to toxins In plants: soil acidity
1. Trish is Type B and her son, Len, is type AB. What is Ron's blood type? How do you know? 2. Is it possible for Janis and John to have a child who is type O? How can you explain this? 3. Is it possible for Stacie and Harry to have a child who is type O?
What about Huntington’s disease? • DOMINANT allele! • Chromosome 4 • Memory, emotional issues, muscle spasms, mental illness, death • Not until 30-40 yrs old
12.2 B: Human Genetics Genetic Testing and Diseases