Patterns of inheritance

1. Genetics & Patterns of inheritance

2. Family resemblance - Habsburgs of Europe Maternal homologue Paternal homologue Haploid sperm Ferdinand II, Holy Roman Emperor, ~1620 Maximilian I, Holy Roman Emperor, 1530 Rudolf II, Holy Roman Emperor, ~1590 Konstanze, queen of Poland, 1604 Family resemblance has long been noted and commented on

3. Inheritance – a historical perspective • Until the middle ages people thought bizarre composite animals could result from breeding widely different species • The giraffe (Giraffacamelopardalis) was once thought to have resulted from a camel breeding with a leopard • Also, species were thought to have been maintained without significant change since the time of their creation Constancy of species - Variation and heredity occur within the boundaries of a species

4. Inheritance – a historical perspective • Constancy of species is false • 1760 - Josef Koelreuter conducted hybridization experiments with different strains of tobacco plants and obtained fertile offspring • Well known animal hybrids include, ligers (lion x tiger), mule (donkey x horse) • Hybridization may produce fertile or sterile offspring depending on genetic compatibility

5. Inheritance – a historical perspective • Inheritance was thought to occur via pangenesis in which particles (pangenes) traveled from different parts of the body to sperm and egg • People also believed that acquired traits or characteristics throughout life were inherited • During the 19th century the idea of blending was popular; traits from parents were thought to be blended together

6. Blending white horse black horse x gray horse

7. Inheritance – a historical perspective Historical ideas about inheritance • Constancy of species • Blending • Acquired traits • Pangenesis • All shown to be false during the mid 1800’s So, how does inheritance actually work?

8. How does inheritance actually work? Gregor Mendel’s experiments • Mendel conducted the first quantitative studies of inheritance • Pure breeding adult peas of different flower colors were crossed • Flower color is a trait - an observable characteristic Mendel was an Austrian monk

9. How does inheritance actually work? Gregor Mendel’s experiments • Crossing experiment: PurpleX White Purple • All offspring produced had purple flowers Why were peas used?

10. Mendel used a monohybrid cross What is a monohybrid cross? • Monohybrid cross - A cross between two individuals involving to observe inheritance of one trait Hybridization terminology • P generation – True breeding parents • F1 generation – First generation offspring; resulting from a cross between pure breeding individuals (parents) • F2 generation – Second generation offspring; resulting from a cross between F1 plants

11. Results of Mendel’s monohybrid cross • F1 generation peas had purple flowers • F2 generation peas consisted of mostly purple flowers (3/4) and small number of white flowers (1/4) • Why? F1 F2

12. So, what is the mechanism of inheritance? • Genes code for traits, each gene has two different forms called alleles • Law of segregation – Alleles separate during meiosis; sperm and egg possess one allele for every gene • Genotype – Combination of alleles one has Mendel’s experiments showed that purple flower color is dominant over white

14. So, what is the mechanism of inheritance? • Genotype – Combination of alleles one has • Two forms of alleles – DOMINANT and recessive alleles • Two alleles = two possible phenotypes • Phenotype – Outward appearance expressed by a gene • Dominant vs. recessive… what’s the difference? Mendel’s experiments showed that purple flower color is dominant over white

15. Punnett square • Letters represent alleles, typically the first letter of a word that defines a trait • Capital P forpurple (dominant trait) , lowercase p for white (recessive trait) • Genotypes are either homozygous or heterozygous Punnett square

16. Punnett square • Punnett square – A tool developed by Reginald Punnett used to predict the number and variety of genetic combinations • Homozygous – Having the same two alleles for one gene (either both dominant or both recessive) • Heterozygous – Having two different alleles for one gene (one dominant allele, and one recessive allele) Reginald Punnett

17. Dihybrid crossing • Mendel did not know if 2+ traits were inherited together or separately • If inherited together phenotypic ratio of the F2 generation would be 3:1 (dependent assortment) • In other words, were dominant alleles inherited together and were recessive alleles inherited together?

18. Dihybrid crossing P F1 • Dihybrid cross – Breeding individuals having for to observed inheritance of two different traits • For example, seed color (yellow, green) and seed texture (round, wrinkled) • Independent assortment – each pair of alleles segregates independently of the other pairs of alleles during meiosis F2

19. Both segregation and independent assortment are explained by the distribution of chromosomes during meiosis

20. Other inheritance patterns Mendel’s experiments illustrate complete dominance offspring always resembled one of the two parents Dominant allele had the same phenotypic effect whether present in one or two copies Incomplete dominance - heterozygous individuals have an intermediate phenotype Crossing red and white snap dragons produces pink snap dragons

21. Blending inheritance vs. Particulate inheritance F1 F2 Offspring remain pink Return of parental phenotypes WRONG RIGHT

22. Examples of inherited traits in humans • Many human traits are controlled by alleles which seem to be inherited according to Mendellian inheritance laws • Some of the most obvious traits include straight hairline vs. widow’s peak, straight thumb or hitchhiker’s thumb • Are you dominant or recessive for such traits? Widow’s peak Hitchhiker’s thumb

23. Some genes have more than one allele • Blood phenotypes are controlled by a combination of two of three different alleles • Three blood type alleles: i, IA, IB • The alleles for blood types A and B are codominant Blood clumping results when certain antibodies bind to specific antigens

24. Blood groups and blood types • Erythrocytes (red blood cell) have cell-surface proteins called antigens • Blood types are based upon the types of antigens one has • Defensive chemicals called antibodies are produced by your body to protect itself from foreign cells or organisms • Antibodies circulate through the body in the fluidic blood plasma Type A Type B Type AB Type O

25. Sex linkage Mother A A • Some traits are controlled by alleles found on sex chromosomes • These traits are commonly referred to as either X-linked or Y-linked • Use a punnett square to figure out genotypic and phenotypic proportions • Each allele of each sex chromosome written as a superscript a a A A a Father A A Punnett square for sex determination A = dominant allele a = recessive allele

26. Sex-linked disorders and pedigrees Pedigree shows inheritance of traits among family members: Circle = female, Square = male • Sex-linked disorders are caused by genes located on sex chromosomes (usually X chromosome) • Sex-linked disorders and other traits may be traced through a pedigree • Sex-linked disorders includered-greencolor blindness, hemophilia, and Duchenne muscular distrophy • Are males or females mostly affected by such disorders? Pedigree for normal hearing and deafness

27. Autosomal disorders Dominant disorders • Cause: dominant alleles • Dwarfism (Achondroplasia), Alzheimer’s disease, Huntington’s disease • Less common than recessive disorders Recessive disorders • Cause: recessive alleles • Albinism, Cystic fibrosis, Sickle-cell anemia, Tay-Sachs disease • More common than dominant disorders Autosomal disorders are more prevalent in certain geographic regions or cultures

28. Human chromosomes • Let’s look at this again • There are 46 chromosomes (23 homologous pairs) in each somatic cell • 22pairsof autosomes • 1 pairofsex chromosomes • XX = Female, XY = Male • Karyotype- chromosomes are arranged according to shape and size Normal human karyotype

29. Nondisjunction and chromosomal disorders • Nondisjunction– failure of chromosomes to separate and segregate into daughter cells • Nondisjunction may occur during meiosis 1 or meiosis 2 • Abnormal number of chromosomes may result (such as atrisomydisorder like Down’s syndrome) Nondisjunction can cause more significant problems causing the fetus to die

30. Autosomal nondisjunction-related disorders • Down syndrome (Trisomy-21) • Patau syndrome (Trisomy-13) • Edward syndrome (Trisomy-18) • Again, individuals with these disorders have an extra chromosome

31. Nondisjunction and chromosomal disorders • Nondisjunction may also affect sex chromosomes • Sex chromosome disorders include Klinefelter syndrome (XXY, or also XXYY, XXXY) in males, and Turner syndrome (X) in females • These disorders cause poor genital development, and various physical abnormalities such as breast development in men (Klinefelter syndrome), poor breast development in women (Turner Syndrome) • Other abnormalities may occur which produce normal male or normalfemale offspring (XYY, or XXX)

32. Summaryof monohybrid crosses C C c C c c C C C What type of monohybrid cross is this an example of?

33. Summary of monohybrid crosses A B B A A B What type of monohybrid cross is this an example of?

34. Summary of monohybrid crosses What type of monohybrid cross is this an example of?

35. Summary of monohybrid crosses What type of monohybrid cross is this an example of?