Chapter 10 - Genetics

What is Genetics? The study of heredity Heredity: passing of traits from parent to offspring

Study of Genetics Children inherit traits Need to study many generations

Review: Genes Section of DNA on chromosomes Paired 1 from mom & 1 from dad

Gregor Mendel (1857) “Father of Genetics” Discovered patterns of inheritance by breeding pea plants

Mendel’s Experiments Why pea plants? Easy to grow & can be self pollinated Hypothesized that “factors” carry information about traits

Flower Anatomy

Mendel’s Laws Independent Assortment: traits are not inherited together Segregation: Alleles separate when gametes are formed

What We Know Now “Factors” are called genes Different forms of a gene are called alleles Represented by letters Ex. flower color alleles P (purple) or p (white)

Alleles Capital letter = dominant allele Ex. P (purple) Lower case = recessive allele Ex. p (white)

Important Vocabulary Genotype = alleles (letters) that make up that trait Ex. PP Phenotype = physical appearance of trait Ex. Purple

Important Vocabulary (Cont.) Homozygous: two of the same alleles (a.k.a. purebreed) Ex. PP or pp Heterozygous: two different alleles (a.k.a. hybrid) Ex. Pp

Inheritance Of Traits If you inherit one dominant allele the recessive allele will not be expressed

Predicting Our Traits Punnett squares show possible genotypes

Setting up a Punnett Square Alleles from Father g Alleles from Mother g G = Green g = White

Interpreting Punnett Squares Gg Offspring

Interpreting Punnett Squares (Cont.) Offspring are: 100 % Heterozygous Their genotype is Gg Their phenotype is green

Monohybrid Cross: Punnett Squares that analyze only one trait: Depending on the parents alleles they can produce 1 or 2 different gametes for that trait.

Dihybrid Cross: Punnett Squares that analyze two traits: If both parents are homozygous for the two traits only one gamete can be formed (all heterozygous).

Dihybrid Continued: If parents are heterozygous for the two traits than 4 types of alleles from male gametes and 4 types of alleles from female gametes can be formed.

Genotypes: almost all different! Phenotypic Ratio is: 9:3:3:1 Genotypes: almost all different!

Probability Measure of how likely something will occur Ex. What is the probability of getting heads when you flip a coin? Ans. 50%

Probability Punnett squares used to predict the probability of inheriting a trait! Actual data not perfect- larger # of offspring more likely match the results predicted.

Recessive Genetic Disorders Need to inherit two copies of recessive allele Tay Sachs Sickle Cell Anemia

More Recessive Genetic Disorders Cystic Fibrosis Albinism Galactosemia

Dominant Genetic Disorders Only need 1 copy of dominant allele Polydactyly, Marfan Syndrome

More Dominant Genetic Disorders Huntington’s Disease Achondroplasia

Ch 11.2 Complex Patterns of Inheritance Most traits are not simply dominant or recessive

Incomplete Dominance Dominant & recessive traits appear to "blend" Ex. snapdragon flowers red x white = pink RR rr Rr

Incomplete Dominance B B BB BB B Bb Bb b A homozygous dominant black cat is crossed with a gray cat and black is incompletely dominant over white. What is the percentage of having a gray kitten? B B BB BB B Bb Bb b

Incomplete Dominance A gray cat is crossed with another gray cat and black is incompletely dominant over white. Complete a Punnett square and tell me what is the genotypic and phenotypic ratio of that cross? Phenotypic ratio: Genotypic ratio:

Codominance Two traits are both fully seen “Co”= together Ex. Roan Horses have both red & white hairs

Codominance R W R RR RW RR RW R Both alleles should be Capital letters since one is not dominant over another. Cross: Roan Horse X Red Horse R W R RR RW RR RW R

Codominance In humans, wavy hair (CS) results by the co-dominance pattern of curly hair (C) and straight hair (S). What are the possible results if a wavy-haired man and a straight-haired woman have children? List Genotypic and Phenotypic Ratios!

Multiple Alleles Two or more alleles control the phenotype Ex. Human ABO blood groups

Multiple Alleles A woman with type B (heterozygous) blood and a man with type AB blood are expecting a child. What are the possible blood types of the kids?

Multiple Alleles A test was done to determine the biological father of a child. The child’s blood Type is B and the mother’s is Type A. Dude #1 has blood type O and dude # 2 has blood type AB. Which dude is the biological father?

Polygenic Traits Traits that are controlled by multiple genes Ex. height, weight, hair color, skin color

Skin Color At least 7 different Genes make up skin color!

Eye Color

Sex-Linked Traits Carried on sex chromosomes (X and Y) Most are recessive & on X chromosome Color blindness, hemophilia

Sex-Linked Traits (cont.) Affect men more than women Men have only one X chromosome Women can be carriers or affected

Sex-Linked Traits (cont.) Sex Chromosomes for Female are: X X Sex Chromosomes for male are: X Y

Sex-Linked Traits (cont.) Fruit fly eye Color R = Red eyes r or w = white eyes What is the probability of having a white eyed male?

Sex-Linked Traits (cont.) A female fruit fly that is homozygous for red eyes mates with a male who has white eyes. What is the probability of having a female with white eyes?

Sex-Linked Traits (cont.) A woman who is heterozygous for colorblindness has a son with a man who is colorblind. What is the probability that their son will be colorblind?

Polyploidy One or more extra chromosomes. 2n = normal number of chromosomes Humans 46 chromosomes/ 23 pairs 1n = half the number of chromosomes Sperm or Egg 23 chromosomes

Polyploidy Triploid (3n)– 3 complete sets of chromosomes. 46 + 23 = 69 Most plants; sometimes earthworms and goldfish; Humans always Lethal!

Studying Inheritance Karyotype: photographic arrangement of a complete set of chromosomes http://trc.ucdavis.edu/biosci10v/bis10v/media/ch08/karyotype.swf

FROM THIS……..

……TO THIS

Studying Inheritance Chromosomes # 1-22 are autosomes (body chromosomes) Chromosomes # 23 are the sex chromosomes. Looking at a karyotype you can see a chromosome mutation.

______Chromosomal________ Abnormalities 1 infant in 200 newborns has a chromosomal abnormality 28% of first trimester miscarriages have a chromosomal abnormality Abnormalities in larger chromosomes don’t usually survive 58

____________________________: Change in the ______________ or CHROMOSOMAL MUTATIONS ____________________________: Change in the ______________ or ____________ of chromosomes structure number

Homologous chromosomes ________________ during MEIOSIS = _________________________ One cell gets 2 copies of the chromosome the other cell gets none. fail to separate NONDISJUNCTION

Nondisjunction 61

Nondisjunction can lead to: Down Syndrome Turner’s Syndrome Klinefelter’s Syndrome

Down syndrome (=____________) TRISOMY 21 63

Down syndrome (Trisomy 21) 1 in 800 births Similar facial features Slanted eyes Protruding tongue 64

Turner syndrome 65

Turner syndrome ____ XO 1 in 5000 births Females have only one X chromosome Small size Slightly decreased intelligence 35% have heart abnormalities Hearing loss common Broad chest Reproductive organs don’t develop at puberty Can’t have children http://medgen.genetics.utah.edu/photographs/diseases/high/611.gif 66

Klinefelter syndrome XXY 67

Klinefelter syndrome 1 in 1000 births Males have extra X chromosomes (Can be XXy, XXXy, or XXXXy) Average to slight decrease in intelligence Small testes/can’t have children Usually not discovered until puberty when don’t mature like peers 68

Obtaining Fetal Cells ~Making a Karyotype~ 1.Amniocentesis: sample of fluid around baby 2.Chorionic Villus Sampling: sample of tissue from the placenta Karyotyping is a technique that can be used at any age. There are many ways to obtain a sample, however we will focus on two samples commonly used to obtain fetal samples. These fetal karyotypes can help determine chromosomal abnormalities before a baby is even born. Amniocentesis Amniocentesis is a process done to obtain a sample from an infant to be karotyped. It is normally considered in situations in which parents are at risk of having an infant with a genetic disorder. This includes situations of advanced maternal age, parents who have had a previous child with chromosomal problems and parents with the presence of a chromosomal translocation or rearrangement. More than 100 biochemical disorders can be tested through amniocentesis. (2) During this procedure, amniotic fluid, which surrounds the baby and provides protection, is taken from the amniotic sac by a long needle inserted into the woman’s abdomen. The body will make more amniotic fluid to replace the fluid removed in the procedure. (2) Chorionic Villus Sampling Chorionic villus sampling is another procedure used to help determine genetic disorders present in the fetus. While this procedure is recommended for women with the same risk factors as in amniocentesis, it is more specialized than amniocentesis and can be done earlier in pregnancy (during about 10-12 weeks of pregnancy). (2) During this procedure, a small, flexible catheter is inserted through the vagina or abdomen into the uterus and is guided by ultrasound images. A sample is taken from the chorionic villus, the fetal tissue that forms part of the placenta, by suction. (2)

Amniocentesis

Chorionic Villus Sampling

Studying Inheritance (cont.) Pedigree: chart that tracks the inheritance of a trait through multiple generations

F1 = Offspring of P generation F2 = Offspring of F1 generation Generation Symbols P = Parental F1 = Offspring of P generation F2 = Offspring of F1 generation

Generation Symbols (cont.) P Generation F1 Generation F2 Generation

Interpreting the Pedigree Female Carrier Male Affected

Dominant Disorder Example:

Recessive Pedigree Example:

Create A Pedigree: One couple has a son and a daughter with normal pigmentation. Another couple has one son and two daughters with normal pigmentation. The daughter from the first couple has three children with the son of the second couple. Their son and one daughter have albinism; their other daughter has normal pigmentation.