Standard Biology Chapter 27 Human Genetics 27.1 The Role of Chromosomes Very complicated compared to peas!

Chromosome Number Each human sperm and egg has 23 different chromosomes Each human body cell has 46 chromosomes (23 pair) Different organisms have different number of chromosomes- most are paired (Homologous) Table 27-1 Chromosome Number p. 566 (next slide)

Chromosome Number 12 6 Pea 14 7 Onion 16 8 Corn 20 10 White Pine 24 Animal or Plant #Chromosomes Body Cell #Chromosomes Sex Cell Red Clover 12 6 Pea 14 7 Onion 16 8 Corn 20 10 White Pine 24 Cat 38 19 Rabbit 44 22 Chicken 78 39

A Way to Tell Chromosome Number Amniocentesis: a look at chromosomes in fetus Performed 15-20 weeks gestation Needle inserted into mother’s abdomen into amniotic fluid surrounding the fetus. Some fluid removed which also contains cells from the fetus. Cells grown for 10 days, watch for dividing cells.

A Way to Tell Chromosome Number Amniocentesis, cont. Study the dividing cells (easy to see chromosomes as sister chromatids) Arrange chromosomes in a karyotype

Karyotype Chromosome smear Karyotype

Karyotype Ordered arrangement of chromosome pairs by number Largest is #1, smallest is #22 Match up banding pattern on chromosomes Can determine sex of fetus by sex chromosomes XY is male XX is female Y chromosome is much smaller than X

A Way to Tell Chromosome Number Chorionic villi sampling (same idea as amniocentesis) Use a piece of the placenta Can do earlier in pregnancy and get results sooner May not be as accurate

Sex- A Genetic Trait Chromosomes # 1-22 are autosomes Don’t determine sex Are the same in males and females Called non sex or body chromosomes Males are XY so make X sperm and make Y sperm Females are XX so only make X eggs

Sex- A Genetic Trait

Sex- A Genetic Trait Males determine the sex of the child

Standard Biology Chapter 27 Human Genetics 27.2 Human Traits

Humans have many traits: those you can see and those you can’t.

Survey of Human Traits Dominant traits Freckles Dimples

Survey of Human Traits Recessive traits Attached ear lobes Straight hair Nonroller tongue Short eyelashes

Survey of Human Traits L=long eyelash trait l=short eyelash trait Both parents are heterozygous and have long eyelashes Expect 3:1 long to short eyelashes in offspring or expressed as a %, expect 75% long eyelashes children and 25% short eyelashes children

Survey of Human Traits L=long eyelash trait l=short eyelash trait Both parents are heterozygous and have long eyelashes L LL Ll l ll Ll

Incomplete Dominance One trait not completely dominant over the other Heterozygotes show in between trait Example: Snapdragon flower color R=red, r=white; Parents are pink (heterozygous)

Incomplete Dominance

Incomplete Dominance Example: Sickle cell Anemia p. 574 RR=round red blood cells R’R’= sickle red blood cells

Incomplete Dominance Sickle cell Anemia Serious health problems because sickle cells cannot carry enough oxygen Causes pain and fatigue (tiredness) because sickle cell block capillaries Sickle cell Anemia most in African Americans

Incomplete Dominance Sickle cell Anemia RR’= both round and sickle red blood cells Usually no health problems because enough health red blood cells to carry oxygen

Blood Types in Humans Blood Type Genes Dominant Recessive A AA or AO O BB or BO AB A and B none OO

Blood Types in Humans Three genes: A, B, and O A and B are dominant to O A and B are codominant

Genes on the X Chromosome Sex chromosomes carry genes X chromosome has many genes because it is a large chromosome Y chromosome has few genes because it is a small chromosome X chromosome and Y chromosome do have the same genes

Genes on the X Chromosome Females are XX have 2 copies of each gene Males are XY have 1 copy of X genes and 1 copy of Y genes

Color Blindness

Color Blindness Color blindness gene on X chromosome p. 576 Red and green shades look alike Females 2 copies of color blindness gene; color blind if both copies are recessive (cc)/ not color blind if heterozygous (Cc) or if homozygous dominant (CC)

Color Blindness Males 1 copy of color blindness gene; color blind if the one is recessive (c)/ not color blind if the one gene is dominant (C) Males are more likely to be color blind Females are carriers when they are heterozygous (Cc) Example: Normal male (XCY), female carrier (XCXc)

Color Blindness Example: Normal male (XCY) female carrier (XCXc) XC XC

Color Blindness Example: Color blind male (XcY), female carrier (XCXc) 50% color blind females 50% color blind males Xc XCXc XcXc Y XCY XcY

Color Blindness This is called a sex-linked genes because it is located on the X chromosome Another sex linked gene is hemophilia (blood clotting disorder)

Standard Biology Chapter 27 Human Genetics 27.3 Genetic Disorders About 600 babies born each day in the U.S. with a disorder, some are genetic disorders.

Errors in Chromosome Number Can happen if baby has more than 46 chromosomes Can happen if baby has less than 46 chromosomes Can happen if sperm or egg have more or less than 23 chromosomes

Errors in Chromosome Number Error happens during meiosis when sister chromatids don’t separate correctly; get one sex cell with 22 the other with 24 chromosomes Can happen to any of your chromosomes

Down Syndrome (Trisomy 21) 3 copies of chromosome #21

Down Syndrome (Trisomy 21) mental retardation, heart problems, facial abnormalities

Down Syndrome (Trisomy 21) 1 in 700 births Increasing incidence with increasing age of mother

Turner’s Syndrome Female with only 1 X chromosome (X0) No neck, short, mental retardation, do not develop secondary sex characteristics 1 in 5000 births

Genetic Disorders and Sex Chromosomes Hemophilia Failure of blood to clot Bruising Significant in royal families of Europe (Russia)

Genetic Disorders and Sex Chromosomes Color blindness Cannot distinguish red/green shades

Genetic Disorders and Autosomes Dyslexia (dominant gene) “Word blindness” See and/or write letters and words backwards, difficult to learn to read

Genetic Disorders and Autosomes PKU- phenylketonuria Amino acid phenylalanine can’t breakdown in body, builds up causing mental retardation Now tested at birth and babies are given special diet with low levels of this amino acid

Genetic Counseling Looks at family history to determine genetic disorder Use of genetics to predict and explain traits in children Genetic counselor- person trained to interpret medical information and counsel patients

Genetic Counseling Answer questions: How did the baby get this disorder? If the baby is healthy, does it have a problem gene? Is the trait dominant or recessive? What will happen to baby’s health as it gets older? What are the chances that future children will have the trait? What medical treatment is available?

Genetic Counseling Genetic counselors use a pedigree (diagram of family history) that can show how a certain trait is passed along in a family

Cystic Fibrosis Recessive genetic disorder Symptoms of disease: excess and thick mucus, respiratory problems and digestive problems Child with the disease 1 in 4 chance if parents are heterozygous F f F FF Ff f Ff ff

Cystic Fibrosis Pedigree 1 2 I II 1 2 3 4 5 1 2 3 4 III 1 2 3 4 IV 5

Pedigree Analysis Are females Are males Shaded in circles and squares are affected individuals Roman Numerals (I – IV) are generations Lines across represent mating Lines down represent offspring

Understanding the Pedigree Count the number of affected males and affected females. If most males and few or no females most likely sex linked trait. Look at the affected individuals. If every individual with the trait has a parent with the trait then this trait is dominant. If non-affected parents produce an offspring with the trait then it is recessive. Determine the phenotype and genotype of every individual

Understanding the Pedigree Affected males: 1 Affected females: 2 No affected individual has parent with the trait, means recessive All affected individuals would be homozygous recessive, aa All parents of affected individuals would be heterozygous, Aa Siblings of affected individuals would be heterozygous (Aa) or homozygous dominant (AA) Means not sex linked

Cystic Fibrosis Pedigree 1 2 I Aa Aa II 1 2 3 4 5 aa ? Aa ? ? 1 2 3 4 III ? ? Aa Aa 1 2 3 4 IV 5 ? aa ? aa ? ? Would be AA or Aa