1. Chapter 6

2. 6.1 Chromosomes and Meiosis
Gametes have half the number of chromosomes that body cells have.

3. 6.1 Chromosomes and Meiosis
You have body cells and gametes
Body cells are also called somatic cells
Germ cells develop into gametes
Germ cells are located in the ovaries and testes
Gametes are sex cells: egg and sperm
Gametes have DNA that can be passed to offspring

4. 6.1 Chromosomes and Meiosis
Your cells have autosomes and sex chromosomes
Your body has 23 pairs of chromosomes.
Homologous pairs of chromosomes have the same structure.
For each homologous pair, one chromosome comes from each parent.

5. 6.1 Chromosomes and Meiosis
Chromosome pairs are autosomes
Sex chromosomes, X and Y, determine gender in mammals

6. 6.1 Chromosomes and Meiosis
Body cells are diploid; gametes are haploid
Fertilization between egg and sperm occurs in sexual reproduction.
Diploid (2n) cells have two copies of every chromosome.
Body cells are diploid
Half the chromosomes come from each parent

7. 6.1 Chromosomes and Meiosis
Haploid (n) cells have one copy of every chromosome.
Gametes are haploid
Gametes have 22 autosomes and 1 sex chromosome.

8. 6.1 Chromosomes and Meiosis
Chromosome number must be maintained in animals.
Many plants have more than two copies of each chromosome.
Mitosis and meiosis are types of nuclear division that make different types of cells.
Mitosis make more diploid cells.

9. 6.1 Chromosomes and Meiosis
Meiosis makes haploid cells from diploid cells
Meiosis occurs in sex cells
Meiosis produces gametes

10. 6.2 Process of Meiosis

11. 6.2 Process of Meiosis
Cells go through two rounds of division in meiosis.
Meiosis reduces chromosome number and creates genetic diversity.

12. 6.2 Process of Meiosis
Meiosis I and meiosis II each have four phases, similar to those in mitosis
Paris of homologous chromosomes separate in meiosis I
Homologous chromosomes are similar but not identical
Sister chromatids divide in meiosis II
Sister chromatids are copies of the same chromosome.

13. 6.2 Process of Meiosis Meiosis I occurs after DNA has been replicated
Meiosis I divides homologous chromosomes in four phases.

15. 6.2 Process of Meiosis
Meiosis II divides sister chromatids in four phases
DNA is not replicated between meiosis I and meiosis II.

17. 6.2 Process of Meiosis
Meiosis differs from mitosis in significant ways
Meiosis has two cell divisions while mitosis has one.
In mitosis, homologous chromosomes never pair up. Meiosis results in haploid cells; mitosis results in diploid cells.

19. 6.2 Process of Meiosis Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Sperm primarily contribute DNA to an embryo.
Sperm become streamlined and motile.
Eggs contribute DNA, cytoplasm, and organelles to an embryo.
During meiosis, the egg gets most of the contents; the other cells form polar bodies.

20. 6.3 Mendel and Heredity

21. 6.3 Mendel and Heredity Mendel laid the groundwork for genetics.
Traits are distinguishing characteristics that are inherited.
Genetics is the study of biological inheritance patterns and variation.
Gregor Mendel showed that traits are inherited as discrete units.
Many in Mendel’s day thought traits were blended.

22. 6.3 Mendel and Heredity
Mendel’s data revealed patterns of inheritance.
Mendel made three key decisions in his experiments.
use of purebred plants
control over breeding
observation of seven “either-or” traits

23. 6.3 Mendel and Heredity
Mendel used pollen to fertilize selected pea plants.
P generation crossed to produce F1 generation
interrupted the self- pollination process by removing male flower parts
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.

24. 6.3 Mendel and Heredity
Mendel allowed the resulting plants to self- pollinate.
Among the F1 generation, all plants had purple flowers
F1 plants are all heterozygous
Among the F2 generation, some plants had purple flowers and some had white

25. 6.3 Mendel and Heredity

26. 6.3 Mendel and Heredity
Mendel observed patterns in the first and second generations of his crosses.

27. 6.3 Mendel and Heredity

28. 6.3 Mendel and Heredity Mendel drew three important conclusions.
purple
white
Mendel drew three important conclusions.
Traits are inherited as discrete units.
Organisms inherit two copies of each gene, one from each parent.
The two copies segregate during gamete formation.
The last two conclusions are called the law of segregation.

29. 6.4 Traits, Genes and Alleles

31. 6.4 Traits, Genes, and Alleles
The same gene can have many versions.
A gene is a piece of DNA that directs a cell to make a certain protein.
Each gene has a locus, a specific position on a pair of homologous chromosomes.

32. 6.4 Traits, Genes, and Alleles
An allele is any alternative form of a gene occurring at a specific locus on a chromosome.
Each parent donates one allele for every gene.
Homologous describes two alleles that are the same at a specific locus.
Heterozygous describes two alleles that are different at a specific locus.

33. Traits, Genes, and Alleles
Genes influence the development of traits
All of an organism’s genetic material is called the genome.
A genotype refers to the makeup of a specific set of genes.
A phenotype is the physical expression of a trait.

34. 6.4 Traits, Genes, and Alleles
Alleles can be represented using letters.
A dominant allele is expressed as a phenotype when at least one allele is dominant.
A recessive allele is expressed as a phenotype only when two copies are present.
Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.

35. 6.4 Traits, Genes, and Alleles
Both homozygous dominant and heterozygous genotypes yield a dominant phenotype.
Most traits occur in a range and do not follow simple dominant-recessive patterns.

37. 6.5 Traits and Probability
Punnett squares illustrate genetic crosses
The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.
The axes represent the possible gametes of each parent.
The boxes show the possible genotypes of the offspring.
The Punnett square yields the ratio of possible genotypes and phenotypes.

38. 6.5 Traits and Probability
A monohybrid cross involves one trait.
Monohybrid crosses examine the inheritance of only one specific trait.
homozygous dominant- homozygous recessive: all heterozygous, all dominant

39. 6.5 Traits and Probability
heterozygous-heterozygous—1:2:1 homozygous dominant: heterozygous: homozygous recessive; 3:1 dominant: recessive

40. 6.5 Traits and Probability
heterozygous-homozygous recessive—1:1 heterozygous: homozygous recessive; 1:1 dominant: recessive
A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.

41. 6.5 Traits and Probability
A dihybrid cross involves two triats
Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio.
Mendel’s dihybrid crosses led to his second law, the law of independent assortment.
The law of independent assortment states that allele pairs separate independently of each other during meiosis.

42. 6.5 Traits and Probability
Heredity patterns can be calculated with probability.
Probability is the likelihood that something will happen.
Probability predicts an average number of occurrences, not an exact number of occurrences.
Probability applies to random events such as meiosis and fertilization.
Record equation on board.

43. 6.6 Meiosis and Genetic Variation
Sexual reproduction creates unique combinations of genes.
Sexual reproduction creates unique combination of genes.
independent assortment of chromosomes in meiosis
random fertilization of gametes
Unique phenotypes may give a reproductive advantage to some organisms.

44. 6.6 Meiosis and Genetic Variation
Crossing over during meiosis increases genetic diversity.
Crossing over is the exchange of chromosome segments between homologous chromosomes.
occurs during prophase I of meiosis I
results in new combinations of genes

45. 6.6 Meiosis and Genetic Variation
Chromosomes contain many genes.
The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over.
Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage.
Genetic linkage allows the distance between two genes to be calculated.

46. 6.6 Meiosis and Genetic Variation