Genetics%20

1

• Genetics study of inheritance of biological
  traits
• Heredity- the passing of traits from parents to
  offspring- biological traits are controlled by
  genes located on chromosomes
• 23 chr. (mom) 23 chr. (dad)
• 46 chr. (you!)

2
Pioneer of Genetics Gregor Mendel


Gregor Mendel was an Austrian monk whose
experiments with garden peas laid the foundation
for the science of genetics
Mendels work provided a basis for understanding
heredity
1822 - 1884
3
Why did Mendel choose the garden pea?


Identifiable characteristics Page 130, Fig 2
Plant reproductionself and cross-fertilizing
4
Plant reproduction


Male Stamen Female Carpel Fertilization
occurs when pollen produced by the stamen
attaches to the carpel, this is known as
pollination
5
Mendel cross-pollinated the pea plants

Started with pure breeding plants those that
only produce identical offspring. Ex) tall
plants only produce other tall plants

6
The first generation was all purple!


The purple trait masked the white flower
trait! F1 generation or first filial
7
Mendels explanation

• He called the purple trait dominant because it
  masked the white trait. He represented it with
  a capital P
• He called the white trait recessive and
  represented it with a lower case p (use cursive
  for lower case letters)
• Each copy of the trait (gene) is called an
  allele, one allele comes from each parent. These
  alleles separate, or segregate, during the
  formation of sex cells.

8
Some more terminology

Allele a version of a gene Genotype refers to
the alleles an organism contains for a particular
trait (Pp) Phenotype refers to the observable
trait (purple) Homozygous a genotype in which
the allelesof a pair are the same Heterozygous
a genotype in which the alleles of apair are
different Monohybrid cross a cross that involves
only one trait

9
Mendel created a second generation by allowing
the F1s to self-pollinate


F1 generation
Pp Pp
Meiosis occurs. Each gamete has one of the
homologous chromosomes.
P p P p
F2 generation inherits alleles from the gametes
of the F1 75 purple, 25 white
10
Cross simulation using Punnett squares

Cross 1 (pure breeding plants)

White parent
pp


Genotypic Ratio 100 Pp heterozygous Phenotypic
Ratio100 purple
PP
Purple parent
11
Cross simulation using Punnett squares

Cross 2 (self pollination)

Purple parent
Pp


PP
Pp
Genotypic Ratio25 PP50 Pp25 pp Phenotypic
Ratio75 purple25 white
Pp
Pp
pp
Purple parent
12
Mendels Laws of Inheritance

• Inherited traits are controlled by a pair (2)
  genes. Each gene can have more than 1 version or
  allele.
• Principle of Dominance- some alleles mask the
  affect of the othere.g. gene hair
  line allele H pointy HH hh h
  straight Hh pointy hairline straight
  hairline
• H dominant masks the other allele so that it
  only appears in offspring
• h recessive only appears in offspring when
  both alleles are h

13
Mendels Laws of Inheritance

3. Law of Segregation- a pair of alleles
separate during the formation of sex cells
independently ? HhBb ? HB Hb hB hb O O O O
Hairline H - point, h - straight Hair colour
B black or brown, b - blonde
14
Mendels Laws of Inheritance

1. Each parent contributes one allele. If a
   pure-breeding plant self-fertilizes, each
   offspring receives two copies of the same allele.
2. Dominant alleles are always expressed when a
   recessive allele is present.
3. Each pair of alleles segregates during the
   formation of sex cells.

15
Practice

Read Chapter 6.1 pp. 154-160 in your
textbook. p. 160 Questions 1-8 Go to
http//dnaftb.org/1/concept and complete the
questions on the worksheet at the class site
http//papaiconomou.weebly.com