Biology – Premed Windsor University School of Medicine and Health Sciences DR. UCHE AMAEFUNA.

CHAPTER 22 Genetics & The Work of Mendel There is more to lectures than the power point slides! Engage your mind

Gregor Mendel used good experimental design used mathematical analysis Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas used good experimental design used mathematical analysis collected data & counted them excellent example of scientific method He studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and a botanist who aroused Mendel’s interest in the causes of variation in plants. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery. The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance.

Mendel’s work ? cross-pollinate true breeding parents Pollen transferred from white flower to stigma of purple flower Bred pea plants cross-pollinate true breeding parents raised seed & then observed traits allowed offspring to self-pollinate & observed next generation all purple flowers result P = parents F = filial generation self-pollinate ?

Looking closer at Mendel’s work true-breeding purple-flower peas true-breeding white-flower peas X Parents 100% 1st generation (hybrids) purple-flower peas In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F1 generation. Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation. self-pollinate 2nd generation 3:1 75% purple-flower peas 25% white-flower peas

What did Mendel’s findings mean? Some traits mask others purple & white flower colors are separate traits that do not blend purple x white ≠ light purple purple masked white dominant allele functional protein affects characteristic masks other alleles recessive allele no noticeable effect allele makes a non-functioning protein I’ll speak for both of us! allele producing functional protein mutant allele malfunctioning protein homologous chromosomes

Genotype vs. phenotype F1 P X purple white all purple Difference between how an organism “looks” & its genetics phenotype description of an organism’s trait genotype description of an organism’s genetic makeup 2 people can have the same appearance but have different genetics: BB vs Bb

PP pp Pp Making crosses x flower color alleles  P or p Can represent alleles as letters flower color alleles  P or p true-breeding purple-flower peas  PP true-breeding white-flower peas  pp F1 P X purple white all purple PP x pp Pp

Traits are inherited as separate units For each trait, an organism inherits 2 copies of a gene, 1 from each parent a diploid organism inherits 1 set of chromosomes from each parent diploid = 2 sets of chromosomes 1 from Mom homologous chromosomes 1 from Dad

Making gametes Remember meiosis! B BB = brown eyes bb = blues eyes BB  brown is dominant over blue  blue is recessive to brown B b Bb

How do we say it? 2 of the same B Homozygous BB BB = brown eyes bb = blues eyes bb b homozygous dominant homozygous recessive 2 different Heterozygous Bb B b Bb = brown eyes

Extending Mendelian genetics Mendel worked with a simple system peas are genetically simple most traits are controlled by single gene each gene has only 2 version 1 completely dominant (A) 1 recessive (a) But its usually not that simple!

Incomplete dominance RR WW RW RR Rr rr RR = red flowers Hybrids have “in-between” appearance RR = red flowers rr = white flowers Rr = pink flowers make 50% less color RR WW RW RR Rr rr

Incomplete dominance P 1st 100% 1:2:1 2nd X generation (hybrids) true-breeding red flowers true-breeding white flowers 100% 100% pink flowers 1st generation (hybrids) self-pollinate 25% white 2nd generation red 1:2:1 50% pink

Co-dominance human ABO blood groups 3 version A, B, i Equal dominance human ABO blood groups 3 version A, B, i A & B alleles are codominant both A & B alleles are dominant over i allele the genes code for different sugars on the surface of red blood cells “name tag” of red blood cell

Quick Review; Johann Gregor Mendel (1822-1884) Father of Genetics Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. Mendel's Laws of Heredity are usually stated as:

1) The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.

2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.

3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant. The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type. Mendel's work and his Laws of Inheritance were not appreciated in his time. It wasn't until 1900, after the rediscovery of his Laws, that his experimental results were understood.

Genetics of Blood type A A A or A i B BB or B i AB O i i Pheno- type Genotype antigen on RBC antibodies in blood donation status A A A or A i type A antigens on surface of RBC anti-B antibodies __ B BB or B i type B antigens on surface of RBC anti-A antibodies AB both type A & type B antigens on surface of RBC no antibodies universal recipient O i i no antigens on surface of RBC anti-A & anti-B antibodies universal donor

Blood donation clotting clotting clotting clotting clotting clotting

One gene: many effects The genes that we have covered so far affect only one trait But most genes affect many traits 1 gene affects more than 1 trait dwarfism (achondroplasia) gigantism (acromegaly) The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic

Many genes: one trait additive effects of many genes humans skin color Polygenic inheritance additive effects of many genes humans skin color height weight eye color intelligence behaviors

Human skin color can produce a wide range of shades AaBbCc x AaBbCc can produce a wide range of shades most children = intermediate skin color some can be very light & very dark

Albinism melanin = universal brown color Johnny & Edgar Winter albino Africans melanin = universal brown color

Environment effect on genes Phenotype is controlled by both environment & genes Coat color in arctic fox influenced by heat sensitive alleles Human skin color is influenced by both genetics & environmental conditions The relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debate a single tree has leaves that vary in size, shape & color, depending on exposure to wind & sun for humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests even identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiences Color of Hydrangea flowers is influenced by soil pH

Genetics of sex Women & men are very different, but just a few genes create that difference In mammals = 2 sex chromosomes X & Y 2 X chromosomes = female: XX X & Y chromosome = male: XY X X X Y

Sex chromosomes

Sex-linked traits especially the X chromosome hemophilia in humans Sex chromosomes have other genes on them, too especially the X chromosome hemophilia in humans blood doesn’t clot Duchenne muscular dystrophy in humans loss of muscle control red-green color blindness see green & red as shades of grey X X Duchenne muscular dystrophy affects one in 3,500 males born in the United States. Affected individuals rarely live past their early 20s. This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin. The disease is characterized by a progressive weakening of the muscles and loss of coordination. X Y

Sex-linked traits XHXh HH XHY x Hh XH Y XHY Y XH XHXH XHXH XH Xh XHY sex-linked recessive XHXh HH XHY x Hh 2 normal parents, but mother is carrier XH Y male / sperm XHY Y XH XHXH XHXH XH Xh female / eggs XHY XHY XHXh XH Xh XHXh XHXh XhY XhY

Hemophilia is a sex-linked recessive trait defined by the absence of one or more clotting factors. These proteins normally slow and then stop bleeding. Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly. Bleeding in muscles and joints can be painful and lead to serious damage. Individuals can be treated with intravenous injections of the missing protein.

Dominant ≠ most common allele Because an allele is dominant does not mean… it is better, or it is more common Polydactyly dominant allele

Polydactyly  only 1 individual out of 500 individuals are born with extra fingers or toes the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive recessive allele far more common than dominant  only 1 individual out of 500 has more than 5 fingers/toes  so 499 out of 500 people are homozygous recessive (aa)