1. Genes, Chromosomes and DNA

2. The structure of DNA
Composed of 4 nucleotide bases, 5 carbon sugar and phosphate.
Base pair = rungs of a ladder.
Edges = sugar-phosphate backbone.
Double Helix
Anti-Parallel

3. The structure of DNA
Figure 2.21

4. DNA Replication Adenine (A) always base pairs with thymine (T)
Guanine (G) always base pairs with Cytosine (C)
Requires steps:
H bonds break as enzymes unwind molecule
New nucleotides (always in nucleus) fit into place beside old strand in a process called Complementary Base Pairing.

5. DNA Replication Figure 2.22a
Remember – the two strands run in opposite directions
Synthesis of a new (daughter) strand occurs in the opposite direction of the old (parental) strand.
Complementary base-pairing occurs
A with T and G with C
G and C have three hydrogen bonds
A and T have two hydrogen bonds

6. DNA Replication
Figure 2.22b

7. DNA Replication Figure 2.22c
New nucleotides joined together by enzyme DNA Polymerase

8. DNA Replication
Each new double helix is composed of an old (parental) strand and a new (daughter) strand.
As each strand acts as a template, process is called Semi-conservative Replication.
Replication errors can occur. Cell has repair enzymes that usually fix problem. An error that persists is a mutation.
This is permanent, and alters the phenotype.

9. Gregor Mendel observed phenotypes and formed hypotheses
How do offspring come to resemble their parents physically?
Genetics begins with the unifying assumption that biological inheritance is carried by structures called Genes.
The same basic patterns of inheritance apply to most organisms.
The inheritance of some human traits can be explained from work on plants
Sex-linked traits in humans is more complicated

10. Terms: Phenotype Genotype An organism’s physical traits
An organism’s genetic makeup

11. Allele
Allele: Alternate form of a gene at same position on pair of chromosomes that affect the same trait.
Dominant Allele: Capital Letter--O
Recessive Allele: lowercase letter--o
Homozygous Dominant--OO
Homozygous Recessive--oo
Heterozygous--Oo

12. Dominant
Recessive
Dominant
Recessive
Pod shape
Inflated
Constricted
Flower color
Purple
White
Pod Color
Green
Yellow
Flower position
Axial
Terminal
Seed color
Yellow
Green
Stem length
Tall
Dwarf
Seed shape
Round
Wrinkled

13. Monohybrid Crosses F2 = 3:1 ratio P Generation (true-breeding parents)
Purple flowers
White flowers
All plants have
purple flowers
F1 Generation
Fertilization
among F1 plants
(F1  F1)
F2 Generation
F2 = 3:1 ratio
3/4 of plants
have purple flowers
1/4 of plants
have white flowers

14. Using a Punnett square to explain the results of a monohybrid cross
P plants PP PP
Using a Punnett square to explain the results of a monohybrid cross
Gametes
All P
All p
F1 plants:
(hybrids)
All Pp
Gametes
1/2 P
1/2 p P P
Eggs
Sperm
F2 plants: p PP p
Phenotypic ratio
3 purple : 1 white Pp Pp pp
Genotypic ratio
1 PP : 2 Pp : 1 pp
Figure 9.8b

15. from the monohybrid crosses, Mendel derived 4 hypotheses…
from the monohybrid crosses, Mendel derived 4 hypotheses….combined, we now refer to these as…
= Mendel’s Principle of Segregation
There are alternative forms of genes, now called alleles
For each characteristic, each organism has two genes
Gametes carry only one allele for each inherited characteristic
Alleles can be dominant or recessive

16. Mendel’s Principle of Independent Assortment
What happens when you follow the inheritance of more than a single trait at one time?
How do two different traits get passed to offspring?
A Dihybrid Cross

17. Dihybrid Cross 9:3:3:1 RrYy RrYy 9/16 3/16 3/16 1/16 RRYY rryy Gametes
Eggs
Sperm
RrYy
RrYy rY rY
RRYY Ry
RrYY
RrYY Ry ry ry
RRYy
rrYY
RRYy
RrYy
RrYy
RrYy
RrYy
Yellow round
9/16
rrYy
RRyy
rrYy
Green round
3/16
Rryy
Rryy
Yellow
wrinkled
3/16
rryy
1/16
Green
wrinkled
9:3:3:1

18. Mendel’s principle of independent assortment
Each pair of alleles segregates independently of the other pairs during gamete formation P a B P a b
Genotype: PP aa Bb

19. Incomplete Dominance in Plants and People
Red RR
White rr
In incomplete dominance F1 hybrids have an appearance in between the phenotypes of the two parents
Gametes R r
Pink Rr
1/2
Gametes
1/2 R r
Eggs
1/2 R
1/2 R
Sperm
Red RR
1/2 r
1/2 r
Pink Rr
Pink rR
White rr
Figure 9.18

20. Types of cells Not all cells of an organisms have the
same number of chromosomes.
Two types of cells:
Somatic Cells
Gametes

21. Somatic Cells Non-sex Cells. Diploid
These cells do not carry genetic information for sexual reproduction.
Contain a full compliment of chromosomes
Characteristic to their species.
Referred to as the diploid number of chromosomes.
Diploid
Means double number.
Designated 2n
All somatic cells in an organism have the 2n or diploid number of chromosomes.

22. Gametes Haploid Sex Cells
Means single number.
Designated n
All gametes formed by an organism have the n or haploid number of
chromosomes.
Sex Cells
Cell which carry genetic information for sexual reproduction.
Contain one half the compliment of chromosomes characteristic to their species.
Referred to as the haploid number of chromosomes.

24. Human Life Cycle Adults produce gametes--egg and sperm.
Gametes fuse to produce zygote.
Zygote grows and develops to produce baby.
Meiosis--process of division that produces gametes.
Mitosis--process of replication and division required for growth.
Adults, zygote and baby--2n. 2n=diploid
Gametes--n. n=haploid

25. Mitosis
Process of division that produces two daughter cells with identical chromosomal content of parent cell.
Mitosis is one stage of the cell cycle.
Cell cycle--cycle of stages a cell goes through in order to grow and divide.
Stages: I=Interphase, Growth 1=G1, DNA synthesis=S, Growth 2=G2, Mitosis=M

26. The Human cell cycle Interphase--G1, S, G2 Mitosis--M G1--growth
S--DNA Synthesis, replication
G2--growth M:
mitosis-- nuclear division
cytokinesis--cell division
pg.339

27. Stages of Division- Mitosis
Prophase--nuclear envelope breakdown, chromosome condensation, spindle formation.
Metaphase--chromosomes are lined up precisely on the metaphase plate, or middle of the cell.
Anaphase--spindle pulls sister chromatids apart.
Telophase--chromatids begin to decondense and become chromatin. Spindle disappears.
Cytokinesis--divide cell and organelles. Actin ring, or cleavage furrow splits cell.

30. Gamete Production -Meiosis
In order to reproduce we must produce gametes.
Gametes are sperm and egg.
Why is that siblings are not identical?
Meiosis blends DNA from parental contributions to produce a mixed up “half” or haploid, set of DNA.
Crossing over is critical for producing haploid DNA with genetic diversity.

31. The Process of Meiosis
Interphase
Haploid gametes are produced in diploid organisms
Two consecutive divisions occur, meiosis I and meiosis II, preceded by interphase
Centrosomes
(with
centriole
pairs)
Nuclear
envelope
Chromatin
Chromosomes duplicate

32. Prophase -I Replicated pairs of chromosomes line up side by side.
These pairs are called Homologous--both have same gene order (gene for eye color, hair color, etc).
Sister chromatid from one pair interact with a Sister chromatid from another pair.
One sister is from father, one sister from mother, but they have same gene order.

33. Prophase -I This interaction is called Synapsis.
Synapsis results in the formation of a Tetrad (4 sisters together).
Crossing over swaps sections of homologous genes.

34. Meiosis - I Figure 2.9 (1) Prophase I Metaphase I Anaphase I
Telophase I

35. Meiosis - II Figure 2.9 (2) Prophase II Metaphase II Anaphase II
Telophase II

36. Meiosis I: Homologous chromosomes separate
Telophase I
and Cytokinesis
Prophase I
Metaphase I
Anaphase I
Sites of crossing over
Microtubules attached to Chromosomes
Sister chromatids
remain attached
Cleavage
furrow
Spindle
Sister
chromatids
Tetrad
Centromere
Homologous chromosomes
pair and exchange segments
Tetrads line up
Pairs of homologous
chromosomes
split up
Two haploid cells form: chromosomes are still double

37. Sister chromatids separate
Meiosis II
Meiosis II:
Sister chromatids separate
Telophase II
and Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Haploid daughter cells
forming
During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes

38. Genes on sex chromosomes determine Sex and sex-linked traits
Micrograph of the chromosomes of an organism paired and numbered.
Used to check for chromosomal abnormalities in individuals.

39. Summary
Genetics is the study of biological traits. These traits are coded for in genes, which are parts of chromosomes.
An Allele is a variant of a gene. These can be dominant or recessive, and these are the basis of inherited traits, both structural and behavioral.
Chromosomes exist as homologous pairs.

40. Summary
Somatic Cells - Non-sex Cells. Contain a full compliment of chromosomes. Characteristic to their species. Referred to as the diploid number of chromosomes.
Gametes - Sex Cells. Cell which carry genetic information for sexual reproduction. Contain one half the compliment of chromosomes characteristic to their species .Referred to as the haploid number of chromosomes.

41. The End.
Any Questions?