Human Genetics Chapter 12

Do you think this trait is dominant or recessive? Human Genetic Traits Do you think this trait is dominant or recessive?

Widow’s Peak? DOMINANT

PTC Tasting Can you taste the PTC???? DOMINANT

RECESSIVE Earlobe Shape? Is your earlobe attached? Do you think this trait is dominant or recessive? RECESSIVE

Dimples? DOMINANT

Human Inheritance Humans - 23 pairs of chromosomes These are made of about 100,000 genes Scientists study disease causing genes because they can easily be traced Pedigree – a family record that shows how a trait is inherited over several generations.

A Pedigree of Hemophilia in the Royal Families of Europe

Pedigree page 299 Carriers – usually, Heterozygous -do not express the recessive allele, but pass it to their offspring Square = Male Circle = Female No shading = normal Shaded = displays trait Half/Half = Carrier

Pedigree Practice Construct a family pedigree of two unaffected parents with a child who suffers from cystic fibrosis.

Pedigree Practice Suppose both parents can roll their tongues but their son cannot. Draw a pedigree showing this trait, and label each symbol with the appropriate genotype.

Pedigree Practice Describe the pedigree of a boy who has galactosemia. His father has galactosemia, his paternal grandparents are phenotypically normal. His mother and maternal grandparents are both phenotypically normal.

A boy is an albino. His mother is also an albino A boy is an albino. His mother is also an albino. His father is phenotypically normal. However, his paternal grandfather is an albino. The other 3 of his grandparents are phenotypically normal.

A brother and a sister both are hemophilic A brother and a sister both are hemophilic. Neither parent shows this trait, however the maternal grandmother suffers from this disorder. The other grandparents are phenotypically normal.

On Your Own Page 300 Mini Lab 11.1 – Investigate Human Pedigrees

Simple Dominant Heredity Many traits are inherited just as the rule of dominance predicts. Remember, in Mendelian inheritance, a single dominant allele inherited from 1 parent is all that is needed for a person to show the dominant trait.

Patterns of Inheritance Traits controlled by a Single Allele >200 traits are determined by a single dominant allele Ex. Huntington’s Disease >250 other traits are determined by homozygous recessive alleles Ex. Cystic Fibrosis, PKU, blue people in Eastern Kentucky

Sometimes Heredity Follows Different Rules 1. Incomplete Dominance: Appearance of a third phenotype 2. Sex-linked inheritance 3. Codominance: Expression of both alleles

1. Incomplete Dominance Incomplete dominance - Cross between organisms with 2 different phenotypes -produces offspring with a 3rd phenotype that is a blending of the parental traits.  RED Flower x WHITE Flower ---> PINK Flower

R = allele for red flowers W = allele for white flowers red x white ---> pink RR x WW ---> 100% RW

2. Sex determination In humans, the diploid number of chromosomes = 46 (23 pairs) There are 22 matching pairs of homologous chromosomes called autosomes. The 23rd pair differs in males and females, they determine the sex of an individual (sex chromosomes) X females (XX) Y males (XY) *Complete a punnett square to determine the expected ratio of males to females produced given their possible gamete contribution

Sex-linked inheritance Traits controlled by genes located on sex chromosomes are called sex-linked traits Sex-Linked Traits are found only on the X chromosome Ex. Hemophilia (recessive) Ex. Patterned Baldness Homozygous baldness-both will lose hair Heterozygous-men will lose hair but women will not Ex. Colorblindness (recessive)

Color Blindness Activty http://colorvisiontesting.com/ishihara.htm http://colorvisiontesting.com/online%20test.htm Draw your family pedigree for color blindness! Predict what your children genotype could be if: Boys – you married a woman who carried the trait for being color blind on her X chromosome Girls – you married a man who was color blind

Patterns of Inheritance Complete a punnett square to show how the allele for red eye color is a sex-linked trait

3. Codominance Codominance - the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms. Example: red x white ---> red & white spotted

R = allele for red flowers W = allele for white flowers red x white ---> red & white spotted RR x WW ---> 100% RW

Examples of Codominance 1. Roan fur in cattle Cattle can be: 1. red (RR = all red hairs) 2. white (WW = all white hairs) 3. roan (RW = red & white hairs together)

2. Human blood type: AB -2 types of protein ("A" & "B") appear together on the surface of blood cells How to determine Blood Types: 4 possible blood types (in order from most common to most rare): O, A, B and AB. O blood type = individual who is homozygous recessive (ii) and does not have an allele for A or B.

Blood types A and B are codominant alleles. Recessive allele i (for blood type O) is only expressed when 2 recessive alleles are present. Individuals who have blood type A: Genotype = IAIA or IAi Individuals who have blood type B: Genotype = IBIB or Ibi Individual who has blood type AB: Genotype = IAIB Individual who has blood type O: Genotype = ii

Human Blood Types

**IMPORTANCE in Real-Life** Blood transfusion can only take place between 2 people who have compatible types of blood. Human blood is separated into different classifications because of the varying proteins on the surface of blood cells. These proteins are there to identify whether or not the blood in the individual's body is it's own and not something the immunity system should destroy.

Blood type practice Use a Punnett Square! A woman has type A blood. Her father has type O blood. The woman marries a man with type O blood. What is the chance that they will have a child with type A blood? What is the chance that the couple from question 1 will have a child with type AB blood? *Show me your answers when you are finished. Keep these in your notes!

Sickle Cell Anemia Read about Codominance on pg. 302-303 Define Codominance. Explain Sickle-cell Disease in ½ page. Complete Data Analysis Lab 11.1 on the bottom ½ of the page.

Sickle Cell Anemia Cont. A Mutation Story: http://www.teachersdomain.org/resource/tdc02.sci.life.gen.lp_disorder/

Nondisjunction Nondisjunction is the failure of homologous chromosome pairs to separate properly during meiosis. The result of this error is a cell with an abnormal (too few or too many) number of chromosomes.

Nondisjunction

Activity: Human Karyotype

Patterns of Inheritance Disorders due to Nondisjunction Monosomy (45 Chromosomes) Trisomy (47 Chromosomes) Trisomy-21 (Down Syndrome) Trisomy-18 (Edwards Syndrome) Trisomy-13 (Patau) Child with Trisomy 21

Disorders due to Nondisjunction Cont. Klinefelter’s (XXY)-male w/ some female traits Turner’s (XO)-female appearance Single Y chromosome do not survive Typically Sterile

Environmental Effects Genes are inherited from parents, but sometimes their expression is modified by environmental factors. An example is the snowshoe hare we discussed earlier in the year-these hares have dark fur in the summer and white fur in the winter.

Snowshoe Hare

Detecting Human Genetic Disorders Genetic Screening – examination of genetic makeup Karyotype: a picture of chromosomes grouped in pairs and arranged in sequence. Screening of Blood: look for certain proteins Genetic Counseling-medical guidance informing of problems that could affect their offspring.

Detecting Human Genetic Disorders Amniocentesis: removal of small amount of amnionic fluid surrounding the fetus Chorionic Villi Sampling: tissue that grows between the mother’s uterus and the placenta (between the 8th and 10th week) Screening Immediately after Birth: Ex PKU (Phenylketonuria)-body cannot metabolize the amino acid phenylalanine Special diet lacking phenylalanine

Karyotyping http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html