Genetics. Ms. Gunjan M. Chaudhari

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1 Genetics Ms. Gunjan M. Chaudhari

2 UNIT 1 Introduction to genetics Genetics:: The scientific study of heredity Heredity : The passing on of characteristics (traits) from parents to offspring

3 Importance of genetics Understanding hereditary diseases and to develop new treatments Donor matches Paternity Forensics Evolution

4 Branches of genetics 1. Microbial genetics- 2. Mycogenetics- 3. PIant genetics- 4. Animal genetics- 5. Human genetics- 6. Population genetics- genetics of the different populations of animal and plant species. 7. Cytogenetics-It provides the cytological explanations of genetical principles. 8. Biochemical genetics-it provides the biochemical explanations of various genetical phenomena.

5 Branches of genetics 9. Molecular genetics- interprets most genetical phenomena in the term of chemical molecules. 10. clinical genetics- genetical analysis in diagnosing various hereditary diseases in man and suggests the possible cures for them. 11. Developmental genetics- genetical knowledge to the developmental biology. 12. Radiation genetics- genetical effects of radiations on the living organisms. 13. Quantitative or biometric genetics- inheritance of quantitative traits such as body weight, mature plant height, egg or milk production records, yield of grain per acre, etc. 14.Ecological genetics- genetics of ecological phenomena

6 Who was Gregor Mendel? Austrian monk who studied mathematics and science

7 The Father of Genetics: Gregor Mendel ( ) * born into a poor peasant family (ethnic minority) * as youth, placed in Catholic monastery

8 The Father of Genetics: Gregor Mendel ( ) * between taught high school biology, and in his spare time experimented with pea plants

9 Mendel s Experiments: * established genetics as a science. * combined careful experiments with mathematical analysis * were ignored,, along with his ideas, during his lifetime

10 Gregor Mendel Austrian Monk. Experimented with pea plants. Used pea plants because: They were available They reproduced quickly They showed obvious differences in the traits Understood that there was something that carried traits from one generation to the next- FACTOR.

11 Mendel was fortunate he chose the Garden Pea Mendel probably chose to work with peas because they are available in many varieties. The use of peas also gave Mendel strict control over which plants mated. Fortunately, the pea traits are distinct and were clearly contrasting.

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13 Genetic Information Gene basic unit of genetic information. Genes determine the inherited characters. Genome the collection of genetic information. Chromosomes storage units of genes. DNA - is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life

14 Mendelian Genetics Dominant traits- traits that are expressed. Recessive traits- traits that are covered up. Alleles- the different forms of a characteristic. Genotype- the types of genes (Alleles) present. Phenotype- what it looks like. Homozygous- two of the same alleles. Heterozygous- two different alleles.

15 Phenotype & Genotype Phenotype - the way an organism looks genotype - the gene combination of an organism

16 Phenotype Genotype

17 Dominant vs. Recessive A dominant allele is expressed even if it is paired with a recessive allele. A recessive allele is only visible when paired with another recessive allele.

18 Heterozygous & Homozygous Heterozygous - if the two alleles for a trait are different (Aa) Homozygous - if the two alleles for a trait are the same (AA or aa)

19 An allele: is one of two or more alternate forms of a gene allele

20 An allele: is one of two or more alternate forms of a gene

21 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 F 1 generation First generation offspring; resulting from a cross between pure breeding individuals (parents) F 2 generation Second generation offspring; resulting from a cross between F 1 plants

22 Results of Mendel s monohybrid cross F 1 generation peas had purple flowers F 2 generation peas consisted of mostly purple flowers (3/4) and small number of white flowers (1/4) Why? F2 F1

23 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

24 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

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

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

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

28 Dihybrid crossing 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 crossing. F 1 F 2 P

29 Mendel s Law of Dominance C. Law of Dominance 1. Of two contrasting characteristics, the dominant one may completely mask the appearance of the recessive one. 29

30 Incomplete Dominance In incomplete dominance, neither allele is dominant so there is a blending of traits when two different alleles for the same trait occur together. Colors blend together heterozygous ( individuals = 3 rd phenotype) red pink white

31 Incomplete Dominance In Four O Clocks, if you cross a red RR (which is always pure) with a white WW (that is also always pure), you get a pink RW (which is always hybrid / heterozygous

32 Incomplete Dominance Cross of two pink flowers RW X RW What are gamete possibilities? genotype ratio 1RR : 2RW : 1WW phenotype ratio 1red : 2 pink : 1 white R R RR red W RW pink W RW pink RW white

33 Codominance Both allele contribute to the phenotype of the organism by showing up simultaneously (at the same time) in heterozygous individuals. In cattle and horses, if you cross a pure _ RR _ with a pure WW you get (RW) which produces the color roan. These cattle or horses actually have both red and white hairs intermixed, or are spotted. Roan is a third _phenotype.

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35 Codominance Andalusian chickens also show this pattern of inheritance. If you cross a black (BB) chicken With a white (WW) chicken You get black+white speckled (BW) chicken

36 Law of segregation Why do traits disappear in one generation only to reappear in a subsequent generation? Each plant possesses two distinct separable units (alleles) for each trait inherited from each parent. Gametes contain ONE allele for each trait. The two alleles for a trait must separate when gametes are formed The unit (allele) does not disappear. It may be present but hidden.

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38 Mendel's Law of Independent Assortment Definition: The principles that govern heredity were discovered by a monk named Gregor Mendel in the 1860's. One of these principles, now called Mendel s Law of Independent Assortment, states that allele pairs separate independently during the formation of gametes. This means that traits are transmitted to offspring independently of one another.

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40 References: 1. www. iteachbio.com 2. www. slideworld.com 3. www. step.nn.k12.va.us an%20exceptions% ppt#257,2,mendel s Principles Revisited 8. Gregor_Mendel.ppt#277,56,Mendel s Law of Dominance