LAB 2 : HUMAN GENETICS

/in /by

1

 

 

 

BIOLOGY102: BIOLOGY, HEALTH AND ENVIIRONMENT LABORATORY

LAB 2 : HUMAN GENETICS

 

Laboratory Exercises:

1) Read background and introductory information on human genetics (inheritance of specific traits, mutations, pedigrees etc).

2) Produce the phenotype and genotype of a unique offspring

3) Record offspring’s genotype

 

Objectives:

Upon completion of today laboratory exercises, a student should be able to:

  • demonstrate an adequate understanding of the variations in human traits
  • describe different human traits and their inheritance from parents to offspring
  • analyze and create human pedigrees
  • characterize different human traits and how they are inherited
  • investigate and produce human pedigrees
  • identify human genetic diseases and how they are inherited
  • comprehend the aim of the Human Genome Project (HPG) and the advantages of genetic data bases

 

 

Background and Introduction:

Inheritance of individual traits in humans has remained a subject of fascination. Humans and other species carry the genes our parents and our grandparents, and during reproduction, these traits are transmitted to our own offspring. At family reunions, it is often fascinating to postulate where Suzi got her red hair and Danny her brown eyes.

A mishap, or mutation in the DNA sequence of a gene can lead to a phenotypical variation in the individual. In some instances, these variations are beneficial, but often these mutations are deleterious, resulting in an organism that is incapable of surviving in its environment, or with genetic disorder. Pedigrees or family histories can be used to trace the presence of a specific defective gene, and the consequent of transmission genetic disorder from parent to offspring.

The entire human genome (all human genes) has been sequenced by scientists and is stored in a data bank for future scientific reference. The sequenced human genome will enable scientists to determine with a high degree of accuracy, defects in an individual’s genetic composition. Detection of such genetic disorders may result in discovery of treatment for many diseases. Although the sequencing of the human genome has many beneficial scientific applications, it is still shrouded with many ethic issues. Accessibility to the stored information in the human genome data bank, control over how and when such information can be used, and use of such information in characterizing individuals as “normal ” and “abnormal”, remain serious issues of concern and public debate.

 

 

 

 

Inheritance of Human Genetic Characteristics

 

Genetic Variation

 

Differences in physical appearance of related individuals are due to variations in genotypes and consequently phenotypes. These variations are also evident in siblings from same parents and twins. However, identical twins will not exhibit such variations. Genotypes (genetic makeup of an individual) are responsible for specific inherited traits. These inherited traits are physically expressed as phenotypes. A pair of gene alleles is responsible for any phenotype expressed, and they transmitted from parents to offspring (Mendelian Law of segregation). In some instances, inherited traits are carried on different chromosomes (rod shaped bodies containing hereditary units or genes). In such cases, the inheritance of one trait is not dependent on the inheritance of another (Mendelian Law of Independent Assortment).

 

 

EXERCISE 1: Visualizing Human Genetic Variation (“Making Your Own Baby”)

 

Materials Needed:

Coin

Characteristics Visualization Handout

 

To demonstrate the incredible variation with the human genome, each student will create the genotype and phenotype of a unique baby (offspring). The pair of alleles responsible for each trait that you will transmit to your baby through your gametes (sex cells) will be randomly selected through coin tossing. For this exercise, you will assume that both parents are heterozygous (have pair of genes with contrasting characters on the chromosome) for each trait. You will record their baby’s (offspring) genotype, and pictorially demonstrate the phenotype. You will use the Visualization Handout provided to help you draw the picture.

 

  • First, choose the gender of your baby. Female = XX, Male = XY. The father’s chromosomes (XY) determine the gender of the baby because an offspring either receives an X or Y chromosomes from the father. On the other hand, the baby will always receive an X chromosome from the mother. For this reason, only one coin toss is needed to determine the sex of the baby. If the coin toss results in a head, the baby receives a Y chromosome from the father, and if a tail, the baby receives an X chromosome.

 

  • On the data sheet (Table 14.1) record your name and the gender of your baby. Then select a name for your baby and record it.

 

  • Now that the gender has been selected, determine the other inherited traits using the illustrations below. For this part of the exercise, you will toss the coin twice (for both the mother & father) to determine which form of their genes will be received by the baby. Note: all parents are heterozygous for traits in this exercise. Coin tosses resulting in heads signify a dominant allele, while tails signify recessive alleles. In situations where the traits exhibit incomplete dominance, a heterozygous baby will demonstrate a new phenotype.

 

  • For each trait, record on your Data Table the genes received from the mother, the genes received from the father, and the resulting genotype of the baby. Additionally, describe the baby’s phenotype.

 

 

 

 

Notes on Polygenic Inheritance

 

Hair Color: Parents are Both AaBbCcDd

 

Hair color is produced by several different genes (polygenic). Suppose that there are 4 genes involved. Therefore, it will take 8 tosses of the coin, representing four for each parent to determine the genotype. The phenotype is determined by the number of dominants as outlined below.

 

8 dominants = black 3 dominants = dark blond

7 dominants = very dark brown 2 dominants = blond

6 dominants = dark brown 1 dominant = light blond

5 dominants = brown 0 dominants = almost white

4 dominants = light brown

 

Eye Color : Parents are Both BbCc

 

Assume two genes for hair color. Therefore, you will toss the coin 4 times, representing two for each parent. The first toss determines the pigment for the front of the iris (represented by B’s) and the second for the pigment behind the iris (represented by C’s). This will be completed twice.

 

BBCC = dark brown BbCC = hazel

BbCc =light brown BBCc = blue gray

Bbcc = light blue bbCC = green

BBcc = dark blue bbCc = light green

bbcc = blue green

 

 

 

 

Name: ____________________________ Lab Day and Time_______________________

 

Parent Name: ___________________________

 

Child’s Name: ___________________ Child’s sex: __________ (heads = boy, tails = girl)

 

Tails-lowercase letters Heads-Capital letters

 

#

Trait

Gene(s) from Mother

Gene(s) from Father

Baby’s Genotype

Baby’s Phenotype

1

Widow’s Peak

W=peak w=no peak

 

 

 

 

2

Eyebrows

E=bushy e=thin

 

 

 

 

3

Eyelashes

Y=long y=short

 

 

 

 

4

Lips

L=full l=thin

 

 

 

 

5

Dimples

D=dimples

d=no dimples

 

 

 

 

6

Nose Shape

N=round n=pointy

 

 

 

 

7

Freckles

F=freckles

f=no freckles

 

 

 

 

8

Face Shape

S=round s=square

 

 

 

 

9

 

Earlobe Attachment

A=attached

a=not attached

 

 

 

 

10

Hair Type

H=curly h=straight

 

 

 

 

11

Eye Size

B=big b=small

 

 

 

 

12

Mouth Length

M=long m=short

 

 

 

 

13

Nose Size

C=big c=small

 

 

 

 

14

Hair Color

See the previous page

 

 

 

 

15

Eye Color

See the previous page

 
"Looking for a Similar Assignment? Get Expert Help at an Amazing Discount!"