1. GENETICS II: Basic concepts of Genetics
Lecturer: Assistant Professor Betul Akcesme
References:
Kenneth Lange “Mathematical and Statistical Methods for Genetic Analysis”
Jurg Ott “Analysis of Human Genetic Linkage”

2. 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
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DNA - a pair of molecules joined by hydrogen bonds: it is organized as two complementary strands, head-to-toe, with the hydrogen bonds between them. Each strand of DNA is a chain of chemical "building blocks", called nucleotides, of which there are four types:adenide (abbreviated A), cytozyne (C), guanine (G) and thymine (T).

3. Chromosome Logical Structure
Locus – location of a gene/marker on the chromosome.
Allele – one variant form of a gene/marker at a particular locus.
Locus1
Possible Alleles: A1,A2
Locus2
Possible Alleles: B1,B2,B3

4. Human Genome Most human cells contain 46 chromosomes:
2 sex chromosomes (X,Y):
XY – in males.
XX – in females.
22 pairs of chromosomes named autosomes.
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5. Genotypes Phenotypes
At each locus (except for sex chromosomes) there are 2 genes. These constitute the individual’s genotype at the locus.
The expression of a genotype is termed a phenotype. For example, hair color, weight, or the presence or absence of a disease.

6. Genotypes Phenotypes (example)
Eb- dominant allele.
Ew- recessive allele.

7. 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.
Inheritance of alternative forms of traits
Antagonistic pairs of "either-or" traits: e.g. purple or white, yellow or green

8. Mendel crossed pure- breeding lines that differed in only one trait, e
Mendel crossed pure- breeding lines that differed in only one trait, e.g. seed color
Examined phenotypes of F1 progeny and F2 progeny
F1 progeny have only one of the parental traits
Both parental traits reappear in F2 progeny in a 3:1 ratio

9. The Punnett square is a simple way to visualize the segregation and random union of alleles
Each F1 hybrid produces two kinds of gametes in a 1:1 ratio
F2 progeny
3:1 ratio of phenotypes
1/4 will breed true for the dominant trait
1/2 will be hybrids
1/4 will breed true for the recessive trait
Fig. 2.11

10. One Locus Inheritance A | A a | a A | a 4 A | a 6 Female Male2 1
A | A
a | a
A | a 3 4
A | a 5 6
Male
Female
heterozygote
homozygote

11. Definitions of commonly used terms
Phenotype is an observable characteristic (e.g. yellow or green pea seeds)
Genotype is a pair of alleles in an individual (e.g. YY or Yy)
Homozygote has two identical alleles (e.g. YY or yy)
Heterozygote has two different alleles (e.g. Yy)
The heterozygous phenotype defines the dominant allele (e.g. Yy peas are yellow, so the yellow Y allele is dominant to the green y allele)
A dominant allele with a dash represents an unknown genotype (e.g. Y− stands for either YY or Yy)

12. Mendel’s 1st Law (Law of Segregation)
Two members of a gene pair segregate from each other into the gametes,
so half the gametes carry one member of the pair and
the other half carry the other member of the pair.
The law of segregation is a principle of Mendelian genetics. The law of segregation occurs during meiosis when gametes are formed. At this time, the alleles for each gene segregate from one another. As a result, each gamete contains only one allele per gene. Thus, the gametes are haploid. The gametes need to be haploid so the specie’s diploid number is maintained when the egg and sperm unite. As a result of the law of segregation, each diploid parent passes a random allele for each trait to his/her offspring during fertilization. Thus, segregation increases variation within a species.
One member of the gene pair segregates into a gamete, thus each gamete only carries one member of the gene pair.

13. Mendel’s 2nd Lawn (Law of independent assortment)
Different gene pairs assort independently in gamete formation.
This “law” is true only in some cases.
Gene pairs on SEPARATE CHROMOSOMES
assort independently at meiosis.
The law of independent assortment followed the law of segregation. The law of independent assortment states that the alleles form each gene segregate independently from one another when gametes are made.
It was later found that linked genes don’t always follow this law. Needless to say, the law of independent assortment also contributes to variation within a species.

14. Law of independent assortment

16. Mendel's Five Laws
I. Traits are a result of different versions of the same gene (alleles). II. Organisms have two copies of each gene. III. During Meiosis, both alleles segregate away from each other (Law of Segregation). IV. If two different alleles are present in the same individual, one version will be observable as the Phenotype (Allele dominance). V. When comparing multiple genes, each allele of each gene will separate into gametes independently of the other (Law of Independent Assortment).

17. Medical Genetics Autosomal recessive Autosomal dominant
When studying rare disorders, 6 general patterns of inheritance are observed:
Autosomal recessive
Autosomal dominant
X-linked recessive
X-linked dominant
Codominant
Mitochondrial

18. Medical Genetics (cont.)
Autosomal recessive
The disease appears in male and female children of unaffected parents.
e.g., cystic fibrosis
Cystic fibrosis – disease affecting the mucus lining of the lungs, leading to breathing problems and other difficulties

19. Medical Genetics (cont.)
Autosomal dominant
Affected males and females appear in each generation of the pedigree.
Affected mothers and fathers transmit the phenotype to both sons and daughters.
e.g., Huntington disease.
Huntington disease - or Huntington's chorea is an inherited disorder characterized by abnormal body movements called chorea, and loss of memory. There also is evidence that doctors as far back as the Middle Ages knew of this devastating disease. The incidence is 5 to 8 per 100,000. It takes its name from the New York physician George Huntington who first described it precisely in 1872.

20. Medical Genetics (cont.)
X-linked recessive
Many more males than females show the disorder.
All the daughters of an affected male are “carriers”.
None of the sons of an affected male show the disorder or are carriers.
e.g., hemophilia
Hemophilia-illness that impair the body's ability to control bleeding.

21. Medical Genetics (cont.)
X-linked dominant
Affected males pass the disorder to all daughters but to none of their sons.
Affected heterozygous females married to unaffected males pass the condition to half their sons and daughters
e.g. fragile X syndrome
Fragile X syndrome - is a genetic condition that causes a range of developmental problems including learning disabilities and mental retardation. Usually males are more severely affected by this disorder than females. In addition to learning difficulties, affected males tend to be restless, fidgety, and inattentive. Affected males also have characteristic physical features that become more apparent with age.

22. Medical Genetics (cont.)
Codominant inheritance
Two different versions (alleles) of a gene can be expressed, and each version makes a slightly different protein
Both alleles influence the genetic trait or determine the characteristics of the genetic condition.
E.g. ABO locus

23. Medical Genetics (cont.)
Mitochondrial inheritance
This type of inheritance applies to genes in mitochondrial DNA
Mitochondrial disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass mitochondrial traits to their children.
E.g. Leber's hereditary optic neuropathy (LHON)

24. MITOSIS
Mitosis is the process by which a cell separates its duplicated genome into two identical halves

25. MITOSIS

26. MITOSIS

27. MEIOSIS
Meiosis is the process that transforms one diploid into four haploid cells.

30. END of the PRESENTATION!!